0001084991-19-000013 | 10-K | XBRL Viewer | Natural GAS Services Group INC

Summary of Significant Accounting Policies (Intangibles) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets [Line Items]
Impairment of goodwill	$ 0	$ 0
Intangibles, net of accumulated amortization	1,401,000	1,526,000
Amortization expense	125,000	125,000	$ 125,000
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2019	125,000
2020	125,000
2021	125,000
2022	125,000
2023	125,000
2024	125,000
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Value	3,159,000	3,159,000
Accumulated Amortization	1,758,000	1,633,000
Net Book Value	1,401,000	1,526,000
Impairment of intangible assets	0	0
Trade Name
Intangible Assets [Line Items]
Indefinite-lived intangible asset, gross carrying value	654,000
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Value	654,000	654,000
Accumulated Amortization	0	0
Net Book Value	$ 654,000	654,000
Developed Technology
Intangible Assets [Line Items]
Intangible assets, useful life	20 years
Intangible assets, weighted average remaining life	6 years
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Value	$ 2,505,000	2,505,000
Accumulated Amortization	1,758,000	1,633,000
Net Book Value	$ 747,000	$ 872,000

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 52,628	$ 69,208
Trade accounts receivable, net of allowance for doubtful accounts of $291 and $569, respectively	7,219	8,534
Inventory	30,974	26,224
Prepaid income taxes	3,148	3,443
Prepaid expenses and other	2,430	817
Total current assets	96,399	108,226
Long-Term Inventory, net of allowance for obsolescence of $19 and $15, respectively	3,980	2,829
Rental equipment, net of accumulated depreciation of $165,428 and $145,851, respectively	175,886	167,099
Property and equipment, net of accumulated depreciation of $11,556 and $11,274, respectively	16,587	7,652
Goodwill	10,039	10,039
Intangibles, net of accumulated amortization of $1,758 and $1,632, respectively	1,401	1,526
Other assets	1,109	939
Total assets	305,401	298,310
Current Liabilities:
Accounts payable	2,122	4,162
Accrued liabilities	8,743	3,106
Deferred income	81	185
Total current liabilities	10,946	7,453
Line of credit	417	417
Deferred income tax liability	32,158	32,163
Other long-term liabilities	1,699	958
Total liabilities	45,220	40,991
Commitments and contingencies (Note 11)
Stockholders’ Equity:
Preferred stock, 5,000 shares authorized, no shares issued or outstanding	0	0
Common stock, 30,000 shares authorized, par value $0.01; 13,005 and 12,880 shares issued and outstanding, respectively	130	129
Additional paid-in capital	107,760	105,325
Retained earnings	152,291	151,865
Total stockholders' equity	260,181	257,319
Total liabilities and stockholders' equity	$ 305,401	$ 298,310

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings
Preferred stock, shares outstanding, beginning of period (in shares) at Dec. 31, 2015		0
Common stock, shares outstanding, beginning of period (in shares) at Dec. 31, 2015			12,603,000
Balance, beginning of period at Dec. 31, 2015	$ 223,981	$ 0	$ 126	$ 98,310	$ 125,545
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options, shares (in shares)			62,000
Exercise of common stock options	1,042		$ 1	1,041
Compensation expense on common stock options	506			506
Issuance of restricted stock, shares (in shares)			99,000
Issuance of restricted stock	0
Tax benefit of equity compensation	72			72
Compensation expense on restricted common stock	1,793		$ 1	1,792
Taxes paid related to net shares settlement of equity awards	(909)			(909)
Net income	6,469				6,469
Preferred stock, shares outstanding, end of period (in shares) at Dec. 31, 2016		0
Common stock, shares outstanding, end of period (in shares) at Dec. 31, 2016			12,764,000
Balance, end of period at Dec. 31, 2016	232,954	$ 0	$ 128	100,812	132,014
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options, shares (in shares)			56,000
Exercise of common stock options	1,120			1,120
Compensation expense on common stock options	363			363
Issuance of restricted stock, shares (in shares)			60,000
Issuance of restricted stock	0
Compensation expense on restricted common stock	3,675		$ 1	3,674
Taxes paid related to net shares settlement of equity awards	(644)			(644)
Net income	$ 19,851				19,851
Preferred stock, shares outstanding, end of period (in shares) at Dec. 31, 2017	0	0
Common stock, shares outstanding, end of period (in shares) at Dec. 31, 2017	12,880,000		12,880,000
Balance, end of period at Dec. 31, 2017	$ 257,319	$ 0	$ 129	105,325	151,865
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options, shares (in shares)			38,000
Exercise of common stock options	680			680
Compensation expense on common stock options	159			159
Issuance of restricted stock, shares (in shares)			87,000
Issuance of restricted stock	0
Compensation expense on restricted common stock	2,226		$ 1	2,225
Taxes paid related to net shares settlement of equity awards	(629)			(629)
Net income	$ 426				426
Preferred stock, shares outstanding, end of period (in shares) at Dec. 31, 2018	0	0
Common stock, shares outstanding, end of period (in shares) at Dec. 31, 2018	13,005,000		13,005,000
Balance, end of period at Dec. 31, 2018	$ 260,181	$ 0	$ 130	$ 107,760	$ 152,291

Stock-Based Compensation (Stock Options Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands			12 Months Ended
	Jun. 16, 2016	Jun. 16, 2009	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 1998
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			0	32,750	0
Weighted average grant date fair value of options granted (in dollars per share)			$ 0	$ 11.93
Total intrinsic value of options exercised			$ 216	$ 446	$ 625
Proceeds from exercise of stock options			680	1,120	1,042
Unrecognized compensation cost related to stock options			131
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense			$ 159	$ 363	$ 506
Unrecognized compensation cost related to stock options, weighted average period for recognition			1 year
Stock Options \| 1998 Stock Option Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			3 years
Award expiration period			10 years
Stock Options \| 1998 Stock Option Plan \| Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized (in shares)	1,000,000.0					550,000
Additional shares authorized (in shares)	250,000	200,000
Number of shares available for grant (in shares)			318,503

Rental Activity

12 Months Ended

Dec. 31, 2018

Leases [Abstract]

Rental Activity

Rental ActivityWe rent natural gas compressor packages to entities in the petroleum industry. These rental arrangements are classified as operating leases and generally have original terms of six months to twenty-four months and continue on a month-to-month basis thereafter. Depreciation expense for rental equipment was $20.9 million, $20.0 million and $20.2 million for the years ended December 31, 2018, 2017 and 2016, respectively. Future minimum rent payments for arrangements not on a month-to-month basis at December 31, 2018 are as follows:


Years Ending December 31,
(in thousands)
2019	$	7,245
2020	$	3,334
2021	$	2,763
2022	$	2,644
2023	$	1,058
Total	$	17,044

Stockholders' Equity (Details) - shares	Dec. 31, 2018	Dec. 31, 2017
Stockholders' Equity Attributable to Parent [Abstract]
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2018
Stockholders' Equity Attributable to Parent [Abstract]
Stockholders' Equity	Stockholders' Equity Preferred Stock We have a total of 5.0 million authorized preferred shares with rights and preferences as designated by the Board of Directors. As of December 31, 2018 and 2017, there were no issued or outstanding preferred shares.

Stock-Based Compensation (Valuation Assumptions) (Details)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk free rate	2.12%
Expected life	6 years
Expected volatility	39.59%
Expected dividend yield	0.00%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Provision for Income Taxes

The provision for income taxes for the years ended December 31, 2018, 2017 and 2016, consists of the following (in thousands):


	2018		2017		2016
Current provision:
Federal	$	(164)	$	3,074	$	4,280
State	(84)		260		429
Total current (benefit) provision	(248)		3,334		4,709
Deferred provision:
Federal expense (benefit)	573		(21,582)		(2,713)

Total deferred expense (benefit)	573		(21,582)		(2,713)
Total expense (benefit) provision	$	325	$	(18,248)	$	1,996

Deferred Tax Assets and Liabilities

The income tax effects of temporary differences that give rise to significant portions of deferred income tax assets and (liabilities) as of December 31, 2018 and 2017, are as follows (in thousands):


	2018		2017
Deferred income tax assets:
Net operating loss carryover	$	2,415	$	—
Stock Compensation	746		843

Other	441		201
Total deferred income tax assets	$	3,602	$	1,044

Deferred income tax liabilities:
Property and equipment	$	(34,968)	(32,377)
Goodwill and other intangible assets	(573)		(604)
Other	(219)		(226)
Total deferred income tax liabilities	(35,760)		(33,207)
Net deferred income tax liabilities	$	(32,158)	$	(32,163)

Effective Income Tax Rate Reconciliation

The effective tax rate for the years ended December 31, 2018, 2017 and 2016, differs from the statutory rate as follows:


	2018		2017		2016
Statutory rate	21.0	%	34.0	%	34.0	%
State and local taxes	1.5	%	1.5	%	1.6	%
Uncertain tax position	72.9	%	—	%	—	%
Research and development credit	(48.3)	%	—	%	(7.5)	%
Stock based compensation	(5.2)	%	(13.4)	%	0.3	%
Nondeductible compensation	4.1	%	—	%	—	%
Domestic production credit	—	%	(14.3)	%	(5.4)	%
Other	(2.7)	%	(1.5)	%	0.6	%
Effective rate	43.3	%	6.3	%	23.6	%
Deferred re-measurement for rate change	—	%	(1,144.4)	%	—	%
Effective rate	43.3	%	(1,138.1)	%	23.6	%

Uncertain tax positions

A reconciliation of the beginning and ending amount of uncertain tax positions is as follows (in thousands):


Balance at January 1, 2018	$	—
Additions based on tax positions related to current year	31
Additions to tax positions of prior years	547


Balance at December 31, 2018	$	578

Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred income tax assets:
Net operating loss carryover	$ 2,415	$ 0
Stock Compensation	746	843
Other	441	201
Total deferred income tax assets	3,602	1,044
Deferred income tax liabilities:
Property and equipment	(34,968)	(32,377)
Goodwill and other intangible assets	(573)	(604)
Other	(219)	(226)
Total deferred income tax liabilities	(35,760)	(33,207)
Net deferred income tax liabilities	$ (32,158)	$ (32,163)

Property and Equipment (Tables)

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment

Property and equipment consists of the following at December 31, 2018 and 2017 (in thousands):


	Useful Lives (Years)	2018		2017
Land	—	$	1,290	$	1,290
Building	39	6,116		6,116
Leasehold improvements	39	808		808
Office equipment and furniture	5	1,492		1,490
Software	5	573		573
Machinery and equipment	7	3,275		3,133
Vehicles	3	6,270		5,516
Construction in Progress	—	8,319		—
Total		28,143		18,926
Less accumulated depreciation		(11,556)		(11,274)
Total		$	16,587	$	7,652

Stock-Based Compensation (Restricted Stock Narrative) (Details) - Restricted Stock - USD ($) $ in Thousands				12 Months Ended
	Mar. 23, 2017	Feb. 14, 2017	Jun. 18, 2014	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)				140,988	126,432	139,451
Share-based compensation expense				$ 2,226	$ 3,675	$ 1,793
Total unrecognized compensation expense				$ 2,620
Unrecognized compensation cost related to stock options, weighted average period for recognition				3 years 3 months
Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)		84,700
Award vesting period		3 years
Chief Financial Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	20,000
Vice President of Technical Services
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	20,000
Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Director
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)				16,288
Award vesting period				1 year
2009 Restricted Stock/Units Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized (in shares)			500,000
Number of shares authorized (in shares)			800,000
Share-based compensation arrangement by share-based payment award, equity instruments other than options, nonvested (in shares)				45,533

Stock-Based Compensation (Stock Options by Exercise Price Range) (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, shares \| shares	283,686
Options outstanding, weighted average remaining contractual life	3 years 6 months 29 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 20.46
Options exercisable, shares \| shares	262,821
Options exercisable, weighted average exercise price (in dollars per share)	$ 19.85
$0.01-15.70
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower limit (in dollars per share)	0.01
Range of exercise prices, upper limit (in dollars per share)	$ 15.70
Options outstanding, shares \| shares	64,852
Options outstanding, weighted average remaining contractual life	6 months 7 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 9.75
Options exercisable, shares \| shares	64,852
Options exercisable, weighted average exercise price (in dollars per share)	$ 9.75
$15.71-17.81
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower limit (in dollars per share)	15.71
Range of exercise prices, upper limit (in dollars per share)	$ 17.81
Options outstanding, shares \| shares	42,000
Options outstanding, weighted average remaining contractual life	1 year 6 months 25 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 17.54
Options exercisable, shares \| shares	42,000
Options exercisable, weighted average exercise price (in dollars per share)	$ 17.54
$17.82-20.48
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower limit (in dollars per share)	17.82
Range of exercise prices, upper limit (in dollars per share)	$ 20.48
Options outstanding, shares \| shares	50,500
Options outstanding, weighted average remaining contractual life	2 years 4 months 2 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 19.43
Options exercisable, shares \| shares	50,500
Options exercisable, weighted average exercise price (in dollars per share)	$ 19.43
$20.49-33.36
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of exercise prices, lower limit (in dollars per share)	20.49
Range of exercise prices, upper limit (in dollars per share)	$ 33.36
Options outstanding, shares \| shares	126,334
Options outstanding, weighted average remaining contractual life	6 years 3 months 25 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 27.33
Options exercisable, shares \| shares	105,469
Options exercisable, weighted average exercise price (in dollars per share)	$ 27.19

Stock-Based Compensation (Summary of Unvested Stock Options) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Unvested, beginning of period (in shares)	48,581
Granted (in shares)	0	32,750	0
Vested (in shares)	(26,549)
Canceled/Forfeited (in shares)	(1,167)
Unvested, end of period (in shares)	20,865	48,581
Weighted Average Grant Date Fair Value
Unvested, beginning of period (in dollars per share)	$ 11.41
Granted (in dollars per share)	0	$ 11.93
Vested (in dollars per share)	10.97
Canceled/Forfeited (in dollars per share)	11.93
Unvested, end of period (in dollars per share)	$ 11.93	$ 11.41

Income Taxes (Uncertain Tax Positions) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018
Uncertain tax positions [Roll Forward]
Balance at January 1, 2018		$ 0
Additions based on tax positions related to current year		31
Additions to tax positions of prior years	$ 547	547
Balance at December 31, 2018	$ 578	$ 578

Commitments and Contingencies

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

401(k) Plan

We offer a 401(k) Plan to all employees that have reached the age of eighteen and have completed six months of service. The participants may contribute up to 100% of their salary subject to IRS limitations. Employer contributions are subject to Board discretion and are subject to a vesting schedule of 20% each year after the first year and 100% after six years. We contributed $355,000, $301,000, and $295,000 to the 401(k) Plan in 2018, 2017 and 2016, respectively.

Rented Facilities, Vehicles and Equipment

We lease certain of our facilities and equipment under operating leases with terms generally ranging from month-to-month to five years. Most leases contain renewal options. Remaining future minimum rental payments (excluding month to month) due under these leases are as follows:


Years Ending December 31, (in thousands)
2019	$	298
2020		118
2021		97
2022		44
2023		35
Thereafter		15
Total	$	607

Rent expense under such leases was $433,000, $310,000, and $325,000 for the years ended December 31, 2018, 2017 and 2016, respectively.

Legal Proceedings

From time to time, we are a party to various legal proceedings in the ordinary course of our business. While management is unable to predict the ultimate outcome of these actions, it believes that any ultimate liability arising from these actions will not have a material effect on our financial position, results of operations or cash flow. We are not currently a party to any bankruptcy, receivership, reorganization, adjustment or similar proceeding, and we are not aware of any other threatened litigation.

Other Long-term Liabilities (Details) - Paint and Coatings - USD ($) $ in Thousands	Jul. 30, 2008	Dec. 31, 2018	Dec. 31, 2017
Other Long-term Liabilities
Long-term purchase commitment, amount	$ 4,800
Cash received from supplier as discount toward future purchases	300
Liability related to deferred discount	$ 300	$ 57	$ 92

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

The provision for income taxes for the years ended December 31, 2018, 2017 and 2016, consists of the following (in thousands):


	2018		2017		2016
Current provision:
Federal	$	(164)	$	3,074	$	4,280
State	(84)		260		429
Total current (benefit) provision	(248)		3,334		4,709
Deferred provision:
Federal expense (benefit)	573		(21,582)		(2,713)

Total deferred expense (benefit)	573		(21,582)		(2,713)
Total expense (benefit) provision	$	325	$	(18,248)	$	1,996

On December 22, 2017, the U.S. government enacted the 2017 Tax Act. The 2017 Tax Act made broad and complex changes to the U.S. tax code that affected the Company’s 2017 financial results. The 2017 Tax Act also established new tax laws that will affect the Company’s financial results after 2017, including a reduction in the U.S. federal corporate income tax rate from 35 percent to 21 percent; additional limitations on the deductibility of executive compensation; limitations on the deductibility of interest; and repeal of the domestic manufacturing deduction. As such, the Company recognized a $18.4 million income tax benefit related to the re-measurement of our deferred tax assets and liabilities in our 2017 financial statements in accordance with SAB 118, which provides SEC staff guidance for the application of ASC 740 in the reporting period in which the 2017 Tax Act was signed into law. We completed our detailed analysis in 2018 with no material adjustments.

The income tax effects of temporary differences that give rise to significant portions of deferred income tax assets and (liabilities) as of December 31, 2018 and 2017, are as follows (in thousands):


	2018		2017
Deferred income tax assets:
Net operating loss carryover	$	2,415	$	—
Stock Compensation	746		843

Other	441		201
Total deferred income tax assets	$	3,602	$	1,044

Deferred income tax liabilities:
Property and equipment	$	(34,968)	(32,377)
Goodwill and other intangible assets	(573)		(604)
Other	(219)		(226)
Total deferred income tax liabilities	(35,760)		(33,207)
Net deferred income tax liabilities	$	(32,158)	$	(32,163)

The effective tax rate for the years ended December 31, 2018, 2017 and 2016, differs from the statutory rate as follows:


	2018		2017		2016
Statutory rate	21.0	%	34.0	%	34.0	%
State and local taxes	1.5	%	1.5	%	1.6	%
Uncertain tax position	72.9	%	—	%	—	%
Research and development credit	(48.3)	%	—	%	(7.5)	%
Stock based compensation	(5.2)	%	(13.4)	%	0.3	%
Nondeductible compensation	4.1	%	—	%	—	%
Domestic production credit	—	%	(14.3)	%	(5.4)	%
Other	(2.7)	%	(1.5)	%	0.6	%
Effective rate	43.3	%	6.3	%	23.6	%
Deferred re-measurement for rate change	—	%	(1,144.4)	%	—	%
Effective rate	43.3	%	(1,138.1)	%	23.6	%

During the fourth quarter of 2018, the Company discovered a potential uncertain tax position attributable to the deductibility of certain executive compensation expense for federal income tax purposes aggregating approximately $168,000, $149,000 and $230,000 for the years ended December 31, 2017, 2016 and 2015, respectively. As a result, in accordance with ASC Topic 740, during the fourth quarter of 2018, the Company recorded a tax adjustment of $547,000 and accrued penalty and interest expense of $55,000 attributable to the uncertain tax position. Management of the Company determined that effect of the potential uncertain tax position on previously reported results of operations for the years ended December 31, 2017 and 2016 was not material.

We account for uncertain tax positions in accordance with guidance in FASB ASC 740, which prescribes the minimum recognition threshold a tax position taken or expected to be taken in a tax return is required to meet before being recognized in the financial statements. A reconciliation of the beginning and ending amount of uncertain tax positions is as follows (in thousands):


Balance at January 1, 2018	$	—
Additions based on tax positions related to current year	31
Additions to tax positions of prior years	547


Balance at December 31, 2018	$	578

Our policy regarding income tax interest and penalties is to expense those items as incurred. During the years ended December 31, 2018, 2017 and 2016, there were no significant income tax interest or penalty items in the statement of income.

We had a regular income tax net operating loss carry forward of $10.7 million for federal income taxes as of December 31, 2018. This net operating loss will be carried forward indefinitely but subject to 80% limitation.

We file income tax returns in the U.S. federal jurisdiction and various state jurisdictions. With few exceptions, we are no longer subject to U.S. federal or state income tax examination by tax authorities for years before 2014.

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Disaggregation of Revenue

The following table shows the Company's revenue disaggregated by product or service type for the years ended:



	Year Ended December 31,
	(in thousands)
	2018		2017		2016
Compressors - sales	$	10,994	$	13,382	$	10,038
Flares - sales	2,535		2,755		1,183
Other (Parts/Rebuilds) - sales	2,740		4,071		2,400
Service and maintenance ¹	20,537		19,857		24,016
Total revenue from contracts with customers	36,806		40,065		37,637
Add: non-ASC 606 rental revenue	28,672		27,628		34,017
Total revenue	$	65,478	$	67,693	$	71,654

¹Service and maintenance includes revenue from servicing our own rental equipment contracted to customers and third party equipment.

Contract with Customer, Asset and Liability

As of December 31, 2018 and December 31, 2017, we had the following receivables and deferred income from contracts with customers:


	December 31, 2018		December 31, 2017
	(in thousands)
Accounts Receivable
Accounts receivable - contracts with customers	$	4,353	$	5,454
Accounts receivable - non-ASC 606	3,157		3,649
Total Accounts Receivable	7,510		9,103
Less: Allowance for doubtful accounts	(291)		(569)
Total Accounts Receivable, net	7,219		8,534

Deferred income	$	81	$	185

Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction

The following table includes estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period:


(in thousands)	2020		2021		2022		2023		2024		Total
Service and Maintenance	$	2,223	$	1,842	$	1,763	$	704	$	—	$	6,532

Schedule of Inventory

At December 31, 2018 and 2017, inventory consisted of the following (in thousands):


	2018		2017
Raw materials - current	$	26,152	$	22,813
Raw materials - long term	3,980		2,829
Finished Goods	1,022		1,022
Work in process	3,800		2,389
Total	$	34,954	$	29,053

Summary of Rental Equipment and Property and Equipment

The

majority of our property and equipment, including rental equipment, is a direct cost to generating revenue and the following table depicts the depreciation associated with each product line at December 31, 2018 , 2017 and 2015 (in thousands):


	2018		2017		2016
Rentals	$	21,588	$	20,861	$	21,325
Sales	265		265		291
Service & Maintenance	22		21		25
Total	$	21,875	$	21,147	$	21,641

Schedule of Identified Finite-Lived Intangible Assets, Finite Lived

The following table represents the identified intangible assets by major asset class (in thousands):


		December 31, 2018										December 31, 2017

	Useful Life (years)	Gross Carrying Value		Accumulated Amortization		Net Book Value		Gross Carrying Value		Accumulated Amortization		Net Book Value



Developed Technology	20	$	2,505	$	1,758	$	747	$	2,505	$	1,633	$	872
Trade Name	Indefinite	654		—		654		654		—		654
Total		$	3,159	$	1,758	$	1,401	$	3,159	$	1,633	$	1,526

Schedule of Identified Indefinite-Lived Intangible Assets

The following table represents the identified intangible assets by major asset class (in thousands):


		December 31, 2018										December 31, 2017

	Useful Life (years)	Gross Carrying Value		Accumulated Amortization		Net Book Value		Gross Carrying Value		Accumulated Amortization		Net Book Value



Developed Technology	20	$	2,505	$	1,758	$	747	$	2,505	$	1,633	$	872
Trade Name	Indefinite	654		—		654		654		—		654
Total		$	3,159	$	1,758	$	1,401	$	3,159	$	1,633	$	1,526

Computation of Basic and Diluted Earnings Per Share

The following table sets forth the computation of basic and diluted earnings per share (in thousands, except per share amounts):


	Year Ended December 31,
	2018		2017		2016
Numerator:
Net income	$	426	$	19,851	$	6,469
Denominator for basic net income per common share:
Weighted average common shares outstanding	12,965		12,831		12,702
Denominator for diluted net income per share:
Weighted average common shares outstanding	12,965		12,831		12,702
Dilutive effect of stock options and restricted shares	268		279		233
Diluted weighted average shares	13,233		13,110		12,935
Earnings per common share:
Basic	$	0.03	$	1.55	$	0.51
Diluted	$	0.03	$	1.51	$	0.50

Other Long-term Liabilities	12 Months Ended
Other Long-term Liabilities	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Other Long-term Liabilities	Other Long-term LiabilitiesWe entered into a purchase agreement with a vendor on July 30, 2008 pursuant to which we agreed to purchase up to $4.8 million of our paint and coating requirements exclusively from the vendor. In connection with the execution of the agreement, the vendor paid us a $300,000 fee which is considered to be a discount toward future purchases from the vendor. The $300,000 payment we received is recorded as a long-term liability and will decrease as the purchase commitment is fulfilled. The long-term liability remaining for the purchase commitment was $57,000 and $92,000 as of December 31, 2018 and 2017, respectively.

Stock-Based Compensation (Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Outstanding, beginning of period (in shares)	327,270	350,186	414,769
Granted (in shares)	0	32,750	0
Exercised (in shares)	(38,250)	(55,666)	(62,083)
Canceled/Forfeited (in shares)	(5,334)		(2,500)
Outstanding, end of period (in shares)	283,686	327,270	350,186	414,769
Exercisable (in shares)	262,821
Weighted Average Grant Date Fair Value
Outstanding, beginning of period (in dollars per share)	$ 20.21	$ 19.45	$ 19.07
Granted (in dollars per share)	0	28.15	0
Exercised (in dollars per share)	17.19	20.12	16.79
Canceled/Forfeited, weighted average exercise price (in dollars per share)	24.02		22.90
Outstanding, end of period (in dollars per share)	20.46	$ 20.21	$ 19.45	$ 19.07
Exercisable (in dollars per share)	$ 19.85
Weighted Average Remaining Contractual Life (years)
Outstanding, weighted average remaining contractual life	3 years 6 months 29 days	4 years 3 months 10 days	4 years 3 months	5 years 29 days
Exercisable, weighted average remaining contractual life	3 years 2 months 19 days
Aggregate Intrinsic Value
Outstanding, aggregate intrinsic value	$ 434	$ 2,255	$ 4,453	$ 1,814
Exercised, aggregate intrinsic value	216	$ 446	625
Canceled/Forfeited, aggregate intrinsic value	0		$ 0
Exercisable, aggregate intrinsic value	$ 434

Retirement of Long-Lived Assets (Details) $ in Thousands	12 Months Ended
Retirement of Long-Lived Assets (Details) $ in Thousands	Dec. 31, 2018 USD ($) compressor	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) compressor
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Loss on retirement of rental equipment	$ 0	$ 0	$ 545
Rental Compressor Unit
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Estimated fair value of long-lived assets		242
Rental Compressor Unit
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Number of units retired \| compressor	13
Number of rental compressors that are not of demanded type, configuration, make or model \| compressor			63
Rental Compressor Unit \| Loss on Retirement of Rental Equipment
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Loss on retirement of rental equipment		$ 545

Summary of Significant Accounting Policies (Property and Equipment) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Work in process	$ 3,800,000	$ 2,389,000
Depreciation	21,875,000	21,147,000	$ 21,641,000
Impairment of long-lived assets held-for-use	$ 0	0	0
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	3 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	39 years
Rental Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful life	15 years
Rentals
Property, Plant and Equipment [Line Items]
Depreciation	$ 21,588,000	20,861,000	21,325,000
Sales
Property, Plant and Equipment [Line Items]
Depreciation	265,000	265,000	291,000
Service & Maintenance
Property, Plant and Equipment [Line Items]
Depreciation	22,000	21,000	$ 25,000
Rental Equipment
Property, Plant and Equipment [Line Items]
Work in process	$ 11,900,000	$ 6,400,000

Credit Facility (Details) - Revolving Credit Facility	12 Months Ended
Credit Facility (Details) - Revolving Credit Facility	Dec. 31, 2018 USD ($) loan
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 30,000,000
Potential increase in borrowing capacity	20,000,000
Potential maximum borrowing capacity	$ 50,000,000
Borrowing base, component, % of eligible accounts receivable	80.00%
Borrowing base, component, % of eligible inventory	50.00%
Borrowing base, allowable share of total commitment amount attributable to inventory component	50.00%
Borrowing base, component, % of eligible equipment inventory	75.00%
Borrowing base amount available	$ 29,500,000
Line of credit	$ 417,000
Weighted average interest rate	3.81%
LIBOR-based Rate
Line of Credit Facility [Line Items]
Variable rate, applicable margin	1.50%
CB Floating Rate
Line of Credit Facility [Line Items]
Variable rate, applicable margin	1.25%
Maximum
Line of Credit Facility [Line Items]
Maximum leverage ratio allowed	2.50
Default trigger, certain defaults of other company indebtedness, amount	$ 50,000
Default trigger, rendering of certain judgments, amount	$ 150,000
Maximum \| LIBOR-based Rate
Line of Credit Facility [Line Items]
Reference rate, number of allowable LIBOR-based borrowings outstanding (in loans) \| loan	3
Minimum
Line of Credit Facility [Line Items]
Minimum commitment coverage ratio allowed	2.00

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2018	Mar. 05, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	NATURAL GAS SERVICES GROUP INC
Entity Central Index Key	0001084991
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		13,193,044
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Public Float			$ 306,723,300

Summary of Significant Accounting Policies (Transaction Price Allocated to the Remaining Performance Obligations (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Accounting Policies [Abstract]
Service and Maintenance	$ 6,532
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Accounting Policies [Abstract]
Service and Maintenance	$ 2,223
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Accounting Policies [Abstract]
Service and Maintenance	$ 1,842
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Accounting Policies [Abstract]
Service and Maintenance	$ 1,763
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Accounting Policies [Abstract]
Service and Maintenance	$ 704
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Accounting Policies [Abstract]
Service and Maintenance	$ 0
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Expected timing of satisfaction, period	1 year

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Organization and Principles of Consolidation

Organization and Principles of ConsolidationThese notes apply to the consolidated financial statements of Natural Gas Services Group, Inc. (the "Company", “NGSG”, "Natural Gas Services Group", "we" or "our") (a Colorado corporation). Natural Gas Services Group was formed on December 17, 1998 for the purposes of combining the operations of certain manufacturing, service and leasing entities. The accompanying consolidated financial statements include the accounts of the Company, its subsidiary, NGSG Properties, LLC and the rabbi trust associated with the Company’s deferred compensation plan, see Note 5. All significant intercompany accounts and transactions for the periods presented have been eliminated in consolidation.

Nature of Operations

Natural Gas Services Group is a leading provider of small to medium horsepower compression equipment to the natural gas industry, with an emerging position in the large horsepower market. We focus primarily on the non-conventional natural gas and oil production business in the United States (such as coal bed methane, gas shale, tight gas and oil shale). We manufacture, fabricate and rent natural gas compressors that enhance the production of natural gas wells. NGSG provides maintenance services for its natural gas compressors. In addition, we sell custom fabricated natural gas compressors to meet customer specifications dictated by well pressures, production characteristics and particular applications. We also manufacture and sell flare systems for oil and natural gas plant and production facilities.

Use of Estimates

The preparation of our consolidated financial statements in conformity with accounting principles generally accepted in the United States of America requires our management to make estimates and assumptions that affect the amounts reported in these consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Significant estimates include fixed asset lives, bad debt allowance and the allowance for inventory obsolescence. Additionally, NGS conducts a yearly review of impairment of long-lived assets. Throughout the review, determining factors are based on estimates that can significantly impact the carrying value of these assets. It is at least reasonably possible these estimates could be revised in the near term and the revisions could be material.

Cash Equivalents

For purposes of reporting cash flows, we consider all short-term investments with an original maturity of three months or less to be cash equivalents.

Accounts Receivable

Our trade receivables consist of customer obligations for the sale of compressors and flare systems due under normal trade terms, and operating leases for the use of our natural gas compressors. The receivables are not collateralized except as provided for under lease agreements. However, we typically require deposits of as much as 50% or use of progress payments for large custom sales contracts. We extend credit based on management's assessment of the customer's financial condition, receivable aging, customer disputes and general business and economic conditions. The allowance for doubtful accounts was $291,000 and $569,000 at December 31, 2018 and 2017, respectively. Management believes that the allowance is adequate; however, actual write-offs may exceed the recorded allowance.

Revenue Recognition

Revenue Recognition Policy

The Company adopted ASC 606, Revenue from Contracts with Customers ("ASC 606") on January, 1, 2018. As a result, the Company has changed its accounting policy for revenue recognition as detailed below.

The Company applied ASC 606 using the cumulative effect method. We had no significant changes in our recognition of revenue at adoption and our review of all open revenue from contracts with customers on January 1, 2018 indicated we had no adjustment to be made. Therefore, our consolidated financial statements for 2017 reported under ASC 605 are comparable to the consolidated financial statements for 2018 reported under ASC 606, since an adjustment was not needed, except for the respective additional disclosures as detailed below.

Revenue is measured based on a consideration specified in a customer’s contract, excluding any sale incentives and taxes collected on behalf of third parties (i.e. sales and property taxes). We recognize revenue once a performance obligation has been satisfied and control over a product or service has transferred to the customer. Shipping and handling costs incurred are accounted for as fulfillment costs and are included in cost of revenues in our condensed consolidated income statement.

Nature of goods and Services

The following is a description of principal activities from which the Company generates its revenue:

Rental Revenue. The Company generates revenue from renting compressors and flare systems to our customers. These contracts may also include a fee for servicing the compressor or flare during the rental contract. Our rental contracts range from six to twenty-four months, with revenue being recognized over time, in equal payments over the term of the contract. After the terms of the contract have expired, a customer may renew their contract or continue renting on a monthly basis thereafter. In accordance with generally accepted accounting principles, the revenue earned from servicing rental equipment is recognized in accordance with ASC 606, while the revenue earned from the rental of the equipment is recognized in accordance with ASC 840 - Leases.

Sales Revenue. The Company generates revenue by the sale of custom/fabricated compressors, flare systems and parts, as well as, exchange/rebuilding customer owned compressors and sale of used rental equipment.

Custom/fabricated compressors and flare systems - The Company designs and fabricates compressors and flares based on the customer’s specifications outlined in their contract. Though the equipment being built is customized by the customer, control under these contracts does not pass to the customer until the compressor or flare package is complete and shipped, or in accordance with a bill and hold arrangements the customer accepts title and assumes the risk and rewards of ownership. We request some of our customers to make progressive payments as the product is being built; these payments are recorded as a contract liability on the Deferred Income line on the consolidated balance sheet until control has been transferred. These contracts also may include an assurance warranty clause to guarantee the product is free from defects in material and workmanship for a set duration of time; this is a standard industry practice and is not considered a performance obligation.

From time to time, upon the customer’s written request, we recognize revenue when manufacturing is complete and the equipment is ready for shipment. At the customer’s request, we will bill the customer upon completing all performance obligations, but before shipment. The customer will formally request we ship the equipment per their direction from our manufacturing facility at a later specified date and that we segregate the equipment from our finished goods, such that they are not available to fill other orders. Per the customer’s agreement change of control is passed to the customer once the equipment is complete and ready for shipment. We have operated using bill and hold agreements with certain customers for many years, with consistent satisfactory results for both the customer and us. The credit terms on these agreements are consistent with the credit terms on all other sales. All control is shouldered by the customer and there are no exceptions to the customer’s commitment to accept and pay for the manufactured equipment. Revenues recognized related to bill and hold arrangements for the years ended December 31, 2018 and 2017 was approximately $8.3 million and $4.6 million, respectively.

Parts - Revenue is recognized after the customer obtains control of the parts. Control is passed either by the customer taking physical possession or the parts being shipped. The amount of revenue recognized is not adjusted for expected returns, as our historical part returns have been de minimis.

Exchange or rebuilding customer owned compressors - Based on the contract, the Company will either exchange a new/rebuilt compressor for the customer’s malfunctioning compressor or rebuild the customer’s compressor. Revenue is recognized after control of the replacement compressor has transferred to the customer by physical delivery, delivery and installment or shipment of the compressor.

Used compressors or flares - From time to time, a customer may request to purchase a used compressor or flare out of our rental fleet. Revenue from the sale of rental equipment is recognized when the control has passed to the customer, when the customer has taken physical possession or the equipment has been shipped.

Service and Maintenance Revenue. The Company provides routine or call-out services on customer owned equipment. Revenue is recognized after services in the contract are rendered.

Payment terms for sales revenue and service and maintenance revenue discussed above are generally 30 to 60 days although terms for specific customers can vary. Also, the transaction prices are not subject to variable consideration constraints.

Contract Costs

The Company applies the practical expedient in ASC 340-40-25-4 and recognizes the incremental costs of obtaining contracts as an expense when incurred if the amortization period of the assets that the Company otherwise would have recognized is one year or less. These costs are included in selling, general and administrative expense on our consolidated income statement.

Major Customers and Concentration of Credit Risk

Major Customers and Concentration of Credit RiskSales and rental income to Occidental Permian, LTD. ("Oxy") in 2018 amounted to 28% of revenue. Sales and rental income to Oxy and Devon Energy Production, Inc. ("Devon") in 2017 amounted to 20% and 15% of revenue, respectively. Sales and rental income to Devon and Oxy in 2016 amounted to 21% and 19% of revenue. No other single customer accounted for more than 10% of our revenues in 2018, 2017 or 2016. Oxy amounted to 26% of our accounts receivable as of December 31, 2018. Oxy amounted to 14% of our accounts receivable as of December 31, 2017. No other customers amounted to more than 10% of our accounts receivable as of December 31, 2018 and 2017.

Inventory

InventoryInventory (current and long-term) is valued at the lower of cost and net realizable value. The cost of inventories is determined by the weighted average method. A reserve is recorded against inventory balances for estimated obsolescence.

Rental Equipment and Property and Equipment

Rental Equipment and Property and EquipmentRental equipment and property and equipment are recorded at cost less accumulated depreciation, except for work-in-progress on new rental equipment which is recorded at cost until it’s complete and added to the fleet. At December 31, 2018 and 2017, we had $11.9 million and $6.4 million in rental equipment work-in-progress, respectively. Depreciation is computed using the straight-line method over the estimated useful lives of the assets. Our rental equipment has an estimated useful life of 15 years, while our property and equipment has an estimate useful lives which range from three to thirty-nine years.

Impairment of Rental Equipment

We assess the impairment of rental equipment and property and equipment whenever events or changes in circumstances indicate that the net recorded amount may not be recoverable. The following factors could trigger an impairment review: significant underperformance relative to historical or projected future cash flows, significant adverse changes in the extent or manner in which asset is being used or its condition, significant negative industry trends or legislative changes prohibiting us from leasing our units or flares. An impairment loss is recognized if the future undiscounted cash flows associated with the asset and the estimated fair value of the asset are less than the asset's carrying value. We recognized no impairments in years ended December 31, 2018, 2017 or 2016.

Gains and losses resulting from sales and dispositions of property and equipment are included in current operations. Maintenance and repairs are charged to operations as incurred.

Goodwill

GoodwillGoodwill represents the cost in excess of fair value of the identifiable net assets acquired. Goodwill is tested for impairment annually or whenever events indicate impairment may have occurred. We performed a qualitative analysis each quarter of 2018 and our annual review was performed in the fourth quarter of 2018.

Intangibles

At December 31, 2018 and 2017, NGSG had intangible assets, which relate to developed technology and a trade name. The carrying amount net of accumulated amortization at December 31, 2018 and 2017 was $1.4 million and $1.5 million, respectively. Developed technology is amortized on a straight-line basis with a useful life of 20 years, with a weighted average remaining life of approximately six years as of December 31, 2018. Amortization expense recognized in each of the years ending December 31, 2018, 2017, and 2016 was $125,000. Estimated amortization expense for the years 2019-2024 is $125,000 per year. NGSG has an intangible asset with a gross carrying value of $654,000 at December 31, 2018 related to the trade name of SCS which was acquired in our acquisition of Screw Compression Systems in January 2005. This asset is not being amortized as it has been deemed to have an indefinite life.

The following table represents the identified intangible assets by major asset class (in thousands):


		December 31, 2018										December 31, 2017

	Useful Life (years)	Gross Carrying Value		Accumulated Amortization		Net Book Value		Gross Carrying Value		Accumulated Amortization		Net Book Value



Developed Technology	20	$	2,505	$	1,758	$	747	$	2,505	$	1,633	$	872
Trade Name	Indefinite	654		—		654		654		—		654
Total		$	3,159	$	1,758	$	1,401	$	3,159	$	1,633	$	1,526

Our policy is to periodically review intangibles for impairment through an assessment of the estimated future cash flows related to such assets. In the event that assets are found to be carried at amounts in excess of estimated undiscounted future cash flows, then the assets will be adjusted for impairment to a level commensurate with a discounted cash flow analysis of the underlying assets. Based upon our analysis, we experienced no impairment of intangible assets during the years ended December 31, 2018 or 2017. Separately, we reviewed our indefinite life intangible for impairment with our goodwill qualitative analysis, which we performed each quarter in 2018 due to a continued decline in our rental utilization and then annually in the

fourth quarter of 2018. Based on this analysis, we experienced no impairment on our indefinite life intangible during the years ended December 31, 2018 or 2017.

Warranty

WarrantyWe accrue amounts for estimated warranty claims based upon current and historical product warranty costs and any other related information known.

Financial Instruments and Concentrations of Credit Risk

We invest our cash primarily in deposits and money market funds with commercial banks. At times, cash balances at banks and financial institutions may exceed federally insured amounts. We believe that the risk to our cash balance is minimal because we have chosen one of the nation’s largest most successful banks, with strong long-term ratings of Aa2/A+/AA.

Per Share Data

Per Share DataBasic earnings per common share is computed using the weighted average number of common shares outstanding during the period. Diluted earnings per common share is computed using the weighted average number of common stock and common stock equivalent shares outstanding during the period.

Income Taxes

Deferred tax assets and liabilities are recognized for the future tax consequences attributable to temporary differences between the financial statement carrying amounts of assets and liabilities and their respective tax bases, and operating losses and tax credit carry-forwards. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled.

ASC Topic 740 prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. In order to record any financial statement benefit, we are required to determine, based on technical merits of the position, whether it is more likely than not (a likelihood of more than 50 percent) that a tax position will be sustained upon examination, including resolution of any related appeals or litigation processes. If that step is satisfied, then we must measure the tax position to determine the amount of benefit to recognize in the financial statements. The tax position is measured at the largest amount of the benefit that is greater than 50 percent likely of being realized upon ultimate settlement. We have no uncertain tax positions as of December 31, 2018 or 2017.

Our policy regarding income tax interest and penalties is to expense those items as other expense.

Fair Value Measurement

Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date under current market conditions. ASC Topic 820 established a fair value hierarchy, which requires an entity to maximize the use of observable inputs when measuring fair value. These inputs are categorized as follows:

Level 1- quoted prices in an active market for identical assets or liabilities;

Level 2- quoted prices in an active market for similar assets or liabilities, inputs other than quoted prices that are observable for similar assets or liabilities, inputs derived principally from or corroborated by observable market data by correlation or other means; and

Level 3- valuation methodology with unobservable inputs that are significant to the fair value measurement.

Management believes that the fair value of our cash and cash equivalents, trade receivables, accounts payable and line of credit at December 31, 2018 and 2017 approximate their carrying values due to the short-term nature of the instruments or the use of prevailing market interest rates.

Segments and Related Information

ASC 280-10-50, “Operating Segments”, define the characteristics of an operating segment as a) being engaged in business activity from which it may earn revenue and incur expenses, b) being reviewed by the company's chief operating decision maker (CODM) for decisions about resources to be allocated and assess its performance and c) having discrete financial information. Although we indeed look at our products to analyze the nature of our revenue, other financial information, such as certain costs and expenses, net income and EBITDA are not captured or analyzed by these categories. Our CODM does not make resource allocation decisions or access the performance of the business based on these categories, but rather in the aggregate. Based on this, management believes that it operates in one business segment.

In their analysis of product lines as potential operating segments, management also considered ASC 280-10-50-11, “Aggregation Criteria”, which allows for the aggregation of operating segments if the segments have similar economic characteristics and if the segments are similar in each of the following areas:

•The nature of the products and services;

•The nature of the production processes;

•The type or class of customer for their products and services;

•The methods used to distribute their products or provide their services; and

•The nature of the regulatory environment, if applicable.

We are engaged in the business of designing and manufacturing compressors and flares. Our compressors and flares are sold and rented to our customers. In addition, we provide service and maintenance on compressors in our fleet and to third parties.These business activities are similar in all geographic areas. Our manufacturing process is essentially the same for the entire Company and is performed in house at our facilities in Midland, Texas and Tulsa, Oklahoma. Our customers primarily consist of entities in the business of producing natural gas. The maintenance and service of our products is consistent across the entire Company and is performed via an internal fleet of vehicles. The regulatory environment is similar in every jurisdiction in that the most impacting regulations and practices are the result of federal energy policy. In addition, the economic characteristics of each customer arrangement are similar in that we maintain policies at the corporate level.

Recently Issued Accounting Pronouncements

On February 25, 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-02, Leases (Topic 842). Under the new guidance, a lessee will be required to recognize assets and liabilities for finance and operating leases with lease terms of more than 12 months. Additionally, this ASU will require disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases, including qualitative and quantitative requirements. The ASU initially required a modified retrospective transition method where a company applies the new leases standard at the beginning of the earliest period presented in the financial statements, but in July 2018 the FASB issued ASU 2018-11. ASU 2018-11 added an optional transition method where a company applies the new leases standard at the adoption date and recognizes a cumulative effect adjustment to the opening balance of retained earnings. For public business entities, the amendments are effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years, with early adoption permitted.

The new standard will be adopted by the Company on January 1, 2019. We anticipate applying certain practical expedients provided by ASU 2016-02 that allow companies to not reassess leases that are in effect prior to adoption, the practical expedient in ASU 2018-11 that allows lessors to not separate lease and non-lease components for certain asset classes and the practical expedient in ASU 2018-20 that allows lessors to exclude third party taxes from lease revenue and lease-related expenses. We have reviewed and evaluated the impact the new standard will have on our accounting policies, internal controls and consolidated balance sheet. In our assessment, we determined an increase in lease assets and lease liabilities on the consolidated balance sheet will be approximately $700,000 at adoption. The adoption by the Company of Topic 842, in regards to the increase in liabilities, will not impact the debt covenants on our existing line of credit, as leases are not considered new indebtedness in our credit agreement as confirmed with our bank. The new standard will create an adjustment to retained earnings produced by the difference in lease assets and lease liabilities brought on to the consolidated balance sheet.

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Allowance for doubtful accounts	$ 291	$ 569
Allowance for inventory obsolescence	19	15
Assets, Noncurrent [Abstract]
Accumulated depreciation, rental equipment	165,428	145,851
Accumulated depreciation, property and equipment	11,556	11,274
Accumulated amortization, intangibles	$ 1,758	$ 1,632
Stockholders' Equity Attributable to Parent [Abstract]
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	30,000,000	30,000,000
Common stock, shares issued (in shares)	13,005,000	12,880,000
Common stock, shares outstanding (in shares)	13,005,000	12,880,000

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Organization and Principles of Consolidation

These notes apply to the consolidated financial statements of Natural Gas Services Group, Inc. (the "Company", “NGSG”, "Natural Gas Services Group", "we" or "our") (a Colorado corporation). Natural Gas Services Group was formed on December 17, 1998 for the purposes of combining the operations of certain manufacturing, service and leasing entities. The accompanying consolidated financial statements include the accounts of the Company, its subsidiary, NGSG Properties, LLC and the rabbi trust associated with the Company’s deferred compensation plan, see Note 5. All significant intercompany accounts and transactions for the periods presented have been eliminated in consolidation.

Nature of Operations

Use of Estimates

Cash Equivalents

For purposes of reporting cash flows, we consider all short-term investments with an original maturity of three months or less to be cash equivalents.

Accounts Receivable

Revenue Recognition Policy

Nature of goods and Services

The following is a description of principal activities from which the Company generates its revenue:

Service and Maintenance Revenue. The Company provides routine or call-out services on customer owned equipment. Revenue is recognized after services in the contract are rendered.

Disaggregation of Revenue

The following table shows the Company's revenue disaggregated by product or service type for the years ended:



	Year Ended December 31,
	(in thousands)
	2018		2017		2016
Compressors - sales	$	10,994	$	13,382	$	10,038
Flares - sales	2,535		2,755		1,183
Other (Parts/Rebuilds) - sales	2,740		4,071		2,400
Service and maintenance ¹	20,537		19,857		24,016
Total revenue from contracts with customers	36,806		40,065		37,637
Add: non-ASC 606 rental revenue	28,672		27,628		34,017
Total revenue	$	65,478	$	67,693	$	71,654

¹Service and maintenance includes revenue from servicing our own rental equipment contracted to customers and third party equipment.

Contract Balances

As of December 31, 2018 and December 31, 2017, we had the following receivables and deferred income from contracts with customers:


	December 31, 2018		December 31, 2017
	(in thousands)
Accounts Receivable
Accounts receivable - contracts with customers	$	4,353	$	5,454
Accounts receivable - non-ASC 606	3,157		3,649
Total Accounts Receivable	7,510		9,103
Less: Allowance for doubtful accounts	(291)		(569)
Total Accounts Receivable, net	7,219		8,534

Deferred income	$	81	$	185

The Company recognized $176,000 in revenue for the period ended December, 2018 that was included in deferred income at the beginning of 2018. For the period ended December 31, 2017, the Company recognized revenue of $1.9 million from amounts related to sales that were included in deferred income at the beginning of 2017.

The increases (decreases) of accounts receivable and deferred income were primarily due to normal timing differences between our performance and the customers’ payments.

Transaction Price Allocated to the Remaining Performance Obligations


(in thousands)	2020		2021		2022		2023		2024		Total
Service and Maintenance	$	2,223	$	1,842	$	1,763	$	704	$	—	$	6,532

All consideration from contracts with customers is included in the amounts presented above.

The Company applies the practical expedient in ASC 606-10-50-14 and does not disclose information about remaining performance obligations that have original expected durations of one year or less.

The Company applies the transition practical expedient in ASC 606-10-65-1(f)(3) and does not disclose the amount of the transaction price allocated to the remaining performance obligations and an explanation of when the Company expects to recognize that amount as revenue for 2018.

Contract Costs

Major Customers and Concentration of Credit Risk

Sales and rental income to Occidental Permian, LTD. ("Oxy") in 2018 amounted to 28% of revenue. Sales and rental income to Oxy and Devon Energy Production, Inc. ("Devon") in 2017 amounted to 20% and 15% of revenue, respectively. Sales and rental income to Devon and Oxy in 2016 amounted to 21% and 19% of revenue. No other single customer accounted for more than 10% of our revenues in 2018, 2017 or 2016. Oxy amounted to 26% of our accounts receivable as of December 31, 2018. Oxy amounted to 14% of our accounts receivable as of December 31, 2017. No other customers amounted to more than 10% of our accounts receivable as of December 31, 2018 and 2017.

Inventory

Inventory (current and long-term) is valued at the lower of cost and net realizable value. The cost of inventories is determined by the weighted average method. A reserve is recorded against inventory balances for estimated obsolescence. This reserve is based on specific identification and historical experience and totaled $19,000 and $15,000 at December 31, 2018 and 2017, respectively. There were 7 newly completed compressor units at December 31, 2018 and December 31, 2017 available for sale or for use in our rental fleet. Our long-term inventory consists of raw materials that remain viable but that the Company does not expect to sell within the next year. At December 31, 2018 and 2017, inventory consisted of the following (in thousands):


	2018		2017
Raw materials - current	$	26,152	$	22,813
Raw materials - long term	3,980		2,829
Finished Goods	1,022		1,022
Work in process	3,800		2,389
Total	$	34,954	$	29,053

Rental Equipment and Property and Equipment

Rental equipment and property and equipment are recorded at cost less accumulated depreciation, except for work-in-progress on new rental equipment which is recorded at cost until it’s complete and added to the fleet. At December 31, 2018 and 2017, we had $11.9 million and $6.4 million in rental equipment work-in-progress, respectively. Depreciation is computed using the straight-line method over the estimated useful lives of the assets. Our rental equipment has an estimated useful life of 15 years, while our property and equipment has an estimate useful lives which range from three to thirty-nine years. The


	2018		2017		2016
Rentals	$	21,588	$	20,861	$	21,325
Sales	265		265		291
Service & Maintenance	22		21		25
Total	$	21,875	$	21,147	$	21,641

Gains and losses resulting from sales and dispositions of property and equipment are included in current operations. Maintenance and repairs are charged to operations as incurred.

Goodwill

Goodwill represents the cost in excess of fair value of the identifiable net assets acquired. Goodwill is tested for impairment annually or whenever events indicate impairment may have occurred. We performed a qualitative analysis each quarter of 2018 and our annual review was performed in the fourth quarter of 2018. We experienced no impairment of goodwill during the years ended December 31, 2018 or 2017.

Intangibles

The following table represents the identified intangible assets by major asset class (in thousands):


		December 31, 2018										December 31, 2017

	Useful Life (years)	Gross Carrying Value		Accumulated Amortization		Net Book Value		Gross Carrying Value		Accumulated Amortization		Net Book Value



Developed Technology	20	$	2,505	$	1,758	$	747	$	2,505	$	1,633	$	872
Trade Name	Indefinite	654		—		654		654		—		654
Total		$	3,159	$	1,758	$	1,401	$	3,159	$	1,633	$	1,526

fourth quarter of 2018. Based on this analysis, we experienced no impairment on our indefinite life intangible during the years ended December 31, 2018 or 2017.

Warranty

We accrue amounts for estimated warranty claims based upon current and historical product warranty costs and any other related information known. The warranty reserve was $22,000 and $65,000 for December 31, 2018 and 2017, respectively, and is included in accrued liabilities on the consolidated balance sheet.

Financial Instruments and Concentrations of Credit Risk

Per Share Data

Basic earnings per common share is computed using the weighted average number of common shares outstanding during the period. Diluted earnings per common share is computed using the weighted average number of common stock and common stock equivalent shares outstanding during the period. There were anti-dilutive securities in 2018, 2017 and 2016.

The following table sets forth the computation of basic and diluted earnings per share (in thousands, except per share amounts):


	Year Ended December 31,
	2018		2017		2016
Numerator:
Net income	$	426	$	19,851	$	6,469
Denominator for basic net income per common share:
Weighted average common shares outstanding	12,965		12,831		12,702
Denominator for diluted net income per share:
Weighted average common shares outstanding	12,965		12,831		12,702
Dilutive effect of stock options and restricted shares	268		279		233
Diluted weighted average shares	13,233		13,110		12,935
Earnings per common share:
Basic	$	0.03	$	1.55	$	0.51
Diluted	$	0.03	$	1.51	$	0.50

In the year-ended December 31, 2018, options to purchase 82,167 shares of common stock with exercise prices ranging from $23.30 to $33.36 were not included in the computation of dilutive income per share, due to their anti-dilutive effect.

In the year-ended December 31, 2017, options to purchase 83,917 shares of common stock with exercise prices ranging from $28.15 to $33.36 were not included in the computation of dilutive income per share, due to their anti-dilutive effect.

In the year-ended December 31, 2016, options to purchase 51,167 shares of common stock with exercise prices ranging from $30.41 to $33.36 were not included in the computation of dilutive income per share, due to their anti-dilutive effect

Income Taxes

Our policy regarding income tax interest and penalties is to expense those items as other expense.

On December 22, 2017, the U.S. government enacted comprehensive tax legislation commonly referred to as the Tax Cuts and Jobs Act (the “2017 Tax Act”), which made broad and complex changes to the U.S. tax code. Certain income tax effects of the 2017 Tax Act are reflected in the Company’s financial results in accordance with Staff Accounting Bulletin No. 118 (“SAB 118”), which provides SEC staff guidance regarding the application of Accounting Standards Codification Topic 740 Income Taxes (“ASC 740”). The effect of this change impacts our effective tax rate. The estimated impact on 2017 was to reduce the deferred tax liabilities by approximately $18.4 million and has been reflected in our effective tax rate reconciliation. At December 31, 2018, we have completed our accounting for the income tax effects of the Tax Act on our deferred tax assets in accordance with the Securities and Exchange Commission Staff Accounting Bulletin No. 118 and ASC 740, and no material adjustments were required.

Fair Value Measurement

Level 1- quoted prices in an active market for identical assets or liabilities;

Level 3- valuation methodology with unobservable inputs that are significant to the fair value measurement.

Segments and Related Information

•The nature of the products and services;

•The nature of the production processes;

•The type or class of customer for their products and services;

•The methods used to distribute their products or provide their services; and

•The nature of the regulatory environment, if applicable.

Recently Issued Accounting Pronouncements

Property and Equipment (Details) $ in Thousands	12 Months Ended
Property and Equipment (Details) $ in Thousands	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) damage	Dec. 31, 2016 USD ($)
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 28,143	$ 18,926
Less accumulated depreciation	(11,556)	(11,274)
Property and equipment, net	16,587	7,652
Depreciation	21,875	$ 21,147	$ 21,641
Number of separate damages \| damage		2
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,290	$ 1,290
Building
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	39 years
Property and equipment, gross	$ 6,116	6,116
Leasehold improvements
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	39 years
Property and equipment, gross	$ 808	808
Office equipment and furniture
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	5 years
Property and equipment, gross	$ 1,492	1,490
Software
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	5 years
Property and equipment, gross	$ 573	573
Machinery and equipment
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	7 years
Property and equipment, gross	$ 3,275	3,133
Vehicles
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	3 years
Property and equipment, gross	$ 6,270	5,516
Construction in Progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	8,319	0
Property, Plant, and Equipment, Excluding Rental Equipment
Property, Plant and Equipment [Line Items]
Depreciation	$ 1,100	$ 1,200	$ 1,400

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Restricted Stock Activity

A summary of all restricted stock/units activity as of December 31, 2016, 2017 and 2018 and changes during the years then ended are presented below.


	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (years)	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2015	145,588	$	19.17	9.12	$	3,246
Granted	139,451	$	21.34	—	$	3,007
Vested	(145,558)	$	19.17	—	$	2,963
Canceled/Forfeited	—	$	—	—	$	—
Outstanding, December 31, 2016	139,451	$	21.34	9.13	$	4,483
Granted	126,432	$	27.06	—	$	3,421
Vested	(81,494)	$	21.20	—	$	2,361
Canceled/Forfeited	—	$	—	—	$	—
Outstanding, December 31, 2017	184,389	$	25.32	8.83	$	4,831
Granted	140,988	24.55		—	3,461
Vested	(110,747)	23.97		—	2,806
Canceled/Forfeited	—	—		—	—
Outstanding, December 31, 2018	214,630	$	25.51	8.85	$	3,529

Stock Options Fair Value Assumptions

The fair value of each option award is estimated on the date of grant using the Black-Scholes option valuation model that uses the assumptions noted in the following table. The risk-free rate for periods within the contractual life of the option is based on the U.S. Treasury yield curve in effect at the time of grant. The expected life of options granted is based on the vesting period and historical exercise and post-vesting employment termination behavior for similar grants. We use historical data to estimate option exercise and employee termination within the valuation model; separate groups of employees that have similar historical exercise behavior are considered separately for valuation purposes.


Weighted average Black -Scholes fair value assumption during the year ended December 31, are as follows:	2017
Risk free rate	2.12	%
Expected life	6 years
Expected volatility	39.59	%
Expected dividend yield	—

Summary of Option Activity

A summary of all option activity as of December 31, 2016, 2017 and 2018 and changes during the years then ended are presented below:


	Number of Shares	Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Life (years)	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2015	414,769	$	19.07	5.08	$	1,814
Granted	—	$	—
Exercised	(62,083)	$	16.79		625
Canceled/Forfeited	(2,500)	$	22.90		$	—
Outstanding, December 31, 2016	350,186	$	19.45	4.25	$	4,453


Granted	32,750	$	28.15
Exercised	(55,666)	$	20.12		446



Outstanding, December 31, 2017	327,270	$	20.21	4.28	$	2,255
Granted	—	—
Exercised	(38,250)	17.19			216
Canceled/Forfeited	(5,334)	24.02			—

Outstanding, December 31, 2018	283,686	$	20.46	3.58	$	434
Exercisable, December 31, 2018	262,821	$	19.85	3.22	$	434

Summary of Stock Options Outstanding

The following table summarizes information about our stock options outstanding at December 31, 2018:


Range of Exercise Prices	Options Outstanding												Options Exercisable
		Shares		Weighted Average Remaining Contractual Life (years)			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price

$0.01-15.70	64,852		0.52		$	9.75		64,852		$	9.75
$15.71-17.81	42,000		1.57		$	17.54		42,000		$	17.54
$17.82-20.48	50,500		2.34		$	19.43		50,500		$	19.43
$20.49-33.36	126,334		6.32		$	27.33		105,469		$	27.19
	283,686		3.58		$	20.46		262,821		$	19.85

Summary of the Status of Unvested Stock Options

The summary of the status of our unvested stock options as of December 31, 2018 and changes during the year then ended is presented below.


Unvested stock options:	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2017	48,581	$	11.41
Granted	—	$	—
Vested	(26,549)	$	10.97
Canceled/Forfeited	(1,167)	$	11.93
Unvested at December 31, 2018	20,865	$	11.93

Summary of Significant Accounting Policies (Inventory) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) compressor	Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Inventory valuation reserves, deductions	$ 19	$ 15
Available-for-sale or rental, compressor units \| compressor	7
Raw materials -current	$ 26,152	22,813
Raw materials - long term	3,980	2,829
Finished Goods	1,022	1,022
Work in process	3,800	2,389
Inventory	$ 34,954	$ 29,053

Related Party	12 Months Ended
Related Party	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party	Related Party In 2016, we entered into a joint venture partnership, N-G, LLC (‘N-G”), with Genis Holdings, LLC (“Genis”) to explore new technologies for wellhead compression. NGS and Genis both share 50% ownership of N-G. In 2018, we ordered some compressor packages from Genis, totaling $1.0 million. The compressors were not completed by December 31, 2018. As of December 31, 2018, we have prepaid $500,000 which is included in prepaid expenses and other in the consolidated balance sheet. The outstanding balance at year end December 31, 2018 is due at the time of completion.

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Rental Payments

Remaining future minimum rental payments (excluding month to month) due under these leases are as follows:


Years Ending December 31, (in thousands)
2019	$	298
2020		118
2021		97
2022		44
2023		35
Thereafter		15
Total	$	607

Stock-Based Compensation

12 Months Ended

Dec. 31, 2018

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation

Restricted Stock/Units

On June 18, 2014, at our annual meeting of shareholders, our shareholders approved a proposed amendment to the 2009 Restricted Stock/Unit Plan (the "Plan") to add additional 500,000 shares of common stock to the Plan, thereby authorizing the issuance of up to 800,000 shares of common stock under the Plan. In accordance with the Company's employment agreement with Stephen Taylor, the Company's Chief Executive Officer, the Compensation Committee reviewed his performance in determining the issuance of restricted common stock. Based on this review which included consideration of the Company's 2017 performance, Mr. Taylor, was awarded 84,700 restricted shares/units on March 15, 2018, which vest over three years, in equal installments beginning March 15, 2019. On March 15, 2018, the Compensation Committee awarded 20,000 restricted shares/units to each G. Larry Lawrence, our CFO, and James Hazlett, our Vice President of Technical Services. The restricted shares/units to Messrs. Hazlett and Lawrence vest over three years, in equal installments, beginning March 15, 2019. We also awarded and issued 16,288 shares of restricted common stock/units to our Board of Directors as partial payment for 2018 directors' fees. The restricted stock/units issued to our directors vests over one year, in quarterly installments, beginning March 31, 2019. Compensation expense related to the restricted shares/units was approximately $2,226,000, $3,675,000 and $1,793,000 for the years ended December 31, 2018, 2017, and 2016, respectively. As of December 31, 2018, there was a total of approximately $2,620,000 of unrecognized compensation expense related to the nonvested portion of these restricted shares/units. This expense is expected to be recognized over the next three years and a quarter. As of December 31, 2018, 45,533 shares were still available for issuance under the Plan.

A summary of all restricted stock/units activity as of December 31, 2016, 2017 and 2018 and changes during the years then ended are presented below.


	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (years)	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2015	145,588	$	19.17	9.12	$	3,246
Granted	139,451	$	21.34	—	$	3,007
Vested	(145,558)	$	19.17	—	$	2,963
Canceled/Forfeited	—	$	—	—	$	—
Outstanding, December 31, 2016	139,451	$	21.34	9.13	$	4,483
Granted	126,432	$	27.06	—	$	3,421
Vested	(81,494)	$	21.20	—	$	2,361
Canceled/Forfeited	—	$	—	—	$	—
Outstanding, December 31, 2017	184,389	$	25.32	8.83	$	4,831
Granted	140,988	24.55		—	3,461
Vested	(110,747)	23.97		—	2,806
Canceled/Forfeited	—	—		—	—
Outstanding, December 31, 2018	214,630	$	25.51	8.85	$	3,529

Stock Option Plan

Our Stock Option Plan which is stockholder approved, permits the granting of stock options to its employees for up to 550,000 shares of common stock. On June 16, 2009, at our annual meeting of shareholders, our shareholders approved to add an additional 200,000 shares of common stock to the Stock Option Plan. On June 16, 2016, at our annual meeting of shareholders, our shareholders approved a proposed amendment to the Stock Option Plan to add an additional 250,000 shares of common stock to the Stock Option Plan, thereby authorizing the issuance of up to 1.0 million shares of common stock under the Stock Option Plan. We believe that such awards better align the interests of our employees with our stockholders. Option awards are generally granted with an exercise price equal to the market price of our stock at the date of grant; those option awards generally vest based on three years of continuous service and have ten-year contractual terms. Certain option and share awards provide for accelerated vesting if there is a change in control of the Company (as defined in the Stock Option Plan). The last date that grants can be made under the Stock Option Plan is February 28, 2026. As of December 31, 2018, 318,503 shares were still available for issue under the Stock Option Plan.


Weighted average Black -Scholes fair value assumption during the year ended December 31, are as follows:	2017
Risk free rate	2.12	%
Expected life	6 years
Expected volatility	39.59	%
Expected dividend yield	—

There were no stock option grants made in 2018 or 2016.

A summary of all option activity as of December 31, 2016, 2017 and 2018 and changes during the years then ended are presented below:


	Number of Shares	Weighted Average Grant Date Fair Value		Weighted Average Remaining Contractual Life (years)	Aggregate Intrinsic Value (in thousands)
Outstanding, December 31, 2015	414,769	$	19.07	5.08	$	1,814
Granted	—	$	—
Exercised	(62,083)	$	16.79		625
Canceled/Forfeited	(2,500)	$	22.90		$	—
Outstanding, December 31, 2016	350,186	$	19.45	4.25	$	4,453


Granted	32,750	$	28.15
Exercised	(55,666)	$	20.12		446



Outstanding, December 31, 2017	327,270	$	20.21	4.28	$	2,255
Granted	—	—
Exercised	(38,250)	17.19			216
Canceled/Forfeited	(5,334)	24.02			—

Outstanding, December 31, 2018	283,686	$	20.46	3.58	$	434
Exercisable, December 31, 2018	262,821	$	19.85	3.22	$	434

The weighted average grant date fair value of options granted during the years was $11.93 in 2017 and none in 2018. The total intrinsic value, or the difference between the exercise price and the market price on the date of exercise, of options exercised during the years ended December 31, 2018, 2017, and 2016 was approximately $216,000, $446,000, and $625,000 respectively. Cash received from stock options exercised during the years ended December 31, 2018, 2017, and 2016 was approximately $680,000, $1.12 million, and $1.0 million, respectively.

The following table summarizes information about our stock options outstanding at December 31, 2018:


Range of Exercise Prices	Options Outstanding												Options Exercisable
		Shares		Weighted Average Remaining Contractual Life (years)			Weighted Average Exercise Price		Shares			Weighted Average Exercise Price

$0.01-15.70	64,852		0.52		$	9.75		64,852		$	9.75
$15.71-17.81	42,000		1.57		$	17.54		42,000		$	17.54
$17.82-20.48	50,500		2.34		$	19.43		50,500		$	19.43
$20.49-33.36	126,334		6.32		$	27.33		105,469		$	27.19
	283,686		3.58		$	20.46		262,821		$	19.85

The summary of the status of our unvested stock options as of December 31, 2018 and changes during the year then ended is presented below.


Unvested stock options:	Shares	Weighted Average Grant Date Fair Value
Unvested at December 31, 2017	48,581	$	11.41
Granted	—	$	—
Vested	(26,549)	$	10.97
Canceled/Forfeited	(1,167)	$	11.93
Unvested at December 31, 2018	20,865	$	11.93

We recognized stock compensation expense from stock options vesting of $159,000, $363,000, and $506,000 for the years ended December 31, 2018, 2017 and 2016, respectively. As of December 31, 2018, there was approximately $131,000 of total unamortized compensation cost related to unvested stock options. We expect to recognize such cost over a weighted-average period of 1.0 year.

There were no stock option grants in 2018.

Rental Activity (Tables)

12 Months Ended

Dec. 31, 2018

Leases [Abstract]

Schedule of Future Minimum Rent Payments Receivable

Future minimum rent payments for arrangements not on a month-to-month basis at December 31, 2018 are as follows:


Years Ending December 31,
(in thousands)
2019	$	7,245
2020	$	3,334
2021	$	2,763
2022	$	2,644
2023	$	1,058
Total	$	17,044

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Revenues	$ 65,478	$ 67,693	$ 71,654
Operating costs and expenses:
Cost of rentals, exclusive of depreciation stated separately below	20,746	18,087	20,350
Cost of sales, exclusive of depreciation stated separately below	12,564	16,286	11,124
Cost of service and maintenance, exclusive of depreciation stated separately below	385	370	398
Loss on retirement of rental equipment	0	0	545
Selling, general and administrative expenses	9,096	10,081	9,011
Depreciation and amortization	22,049	21,302	21,796
Total operating costs and expenses	64,840	66,126	63,224
Operating income	638	1,567	8,430
Other income
Interest expense	(69)	(14)	(8)
Other income	182	50	43
Total other income, net	113	36	35
Income before provision for income taxes	751	1,603	8,465
Provision for income taxes
Current	(248)	3,334	4,709
Deferred	573	(21,582)	(2,713)
Total income tax expense (benefit)	325	(18,248)	1,996
Net income	$ 426	$ 19,851	$ 6,469
Earnings per share:
Earnings per share - Basic (in dollars per share)	$ 0.03	$ 1.55	$ 0.51
Earnings per share - Diluted (in dollars per share)	$ 0.03	$ 1.51	$ 0.50
Weighted average shares outstanding:
Weighted average shares outstanding, Basic (in shares)	12,965	12,831	12,702
Weighted average shares outstanding, Diluted (in shares)	13,233	13,110	12,935
Rental income
Revenue:
Revenues	$ 47,766	$ 46,046	$ 56,717
Sales
Revenue:
Revenues	16,269	20,208	13,621
Service and maintenance income
Revenue:
Revenues	$ 1,443	$ 1,439	$ 1,316

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
401(k) plan, minimum eligibility age	18 years
401(k) plan, requisite service period	6 months
401(k) plan, maximum annual contribution per employee, percent	100.00%
401(k) plan, employer's matching contribution, annual vesting percentage	20.00%
401(k) plan, employer contribution, ultimate vesting percentage	100.00%
401(k) plan, employer's matching contribution, vesting term	6 years
401(k) plan, employer contribution amount	$ 355	$ 301	$ 295
Operating leases, maximum term	5 years
Operating leases, rent expense	$ 433	$ 310	$ 325

Quarterly Financial Data - Unaudited

12 Months Ended

Dec. 31, 2018

Quarterly Financial Data [Abstract]

Quarterly Financial Data

Quarterly Financial Data (in thousands, except per share data) – Unaudited


2018	Q1		Q2		Q3		Q4		Total
Total revenue	$	14,718	$	18,204	$	16,396	$	16,160	$	65,478
Operating income (loss)	350		226		(44)		106		638
Net income (loss)	225		247		236		(282)		426
Net income (loss) per share - Basic	0.02		0.02		0.02		(0.02)		0.03
Net income (loss) per share - Diluted	0.02		0.02		0.02		(0.02)		0.03


2017	Q1		Q2		Q3		Q4		Total
Total revenue	$	18,902	$	16,218	$	15,913	$	16,660	$	67,693
Operating income	343		414		593		217		1,567
Net income ⁽¹⁾	252		375		522		18,702		19,851
Net income per share - Basic	0.02		0.03		0.04		1.46		1.55
Net income per share - Diluted	0.02		0.03		0.04		1.42		1.51

(1) The increase in fourth quarter net income is largely a result of the 2017 Tax Act, see Note 7.

Amounts may not add due to rounding differences.

Quarterly Financial Data - Unaudited (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Data [Abstract]
Total revenue	$ 16,160	$ 16,396	$ 18,204	$ 14,718	$ 16,660	$ 15,913	$ 16,218	$ 18,902	$ 65,478	$ 67,693	$ 71,654
Operating income (loss)	106	(44)	226	350	217	593	414	343	638	1,567	8,430
Net income (loss)	$ (282)	$ 236	$ 247	$ 225	$ 18,702	$ 522	$ 375	$ 252	$ 426	$ 19,851	$ 6,469
Net income (loss) per share - Basic (in dollars per share)	$ (0.02)	$ 0.02	$ 0.02	$ 0.02	$ 1.46	$ 0.04	$ 0.03	$ 0.02	$ 0.03	$ 1.55	$ 0.51
Net income (loss) per share - Diluted (in dollars per share)	$ (0.02)	$ 0.02	$ 0.02	$ 0.02	$ 1.42	$ 0.04	$ 0.03	$ 0.02	$ 0.03	$ 1.51	$ 0.50

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References

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+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Summary of Significant Accounting Policies (Narrative) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Jan. 01, 2019 USD ($)
Revenue from External Customer [Line Items]
Cash equivalents, qualification, maximum original maturity of short-term investments									3 months
Customer deposit requirements, large custom contracts, maximum percentage									50.00%
Allowance for doubtful accounts	$ 291,000				$ 569,000				$ 291,000	$ 569,000
Revenues	16,160,000	$ 16,396,000	$ 18,204,000	$ 14,718,000	16,660,000	$ 15,913,000	$ 16,218,000	$ 18,902,000	65,478,000	67,693,000	$ 71,654,000
Impairment of goodwill									0	0
Product warranty reserves	22,000				65,000				22,000	65,000
Uncertain tax positions	0				$ 0				0	0
Additions to tax positions of prior years	547,000								547,000
Income tax penalties and interest accrued	$ 55,000								$ 55,000
Tax reform impact										18,400,000
Number of business segments \| segment									1
Bill and Hold Arrangement
Revenue from External Customer [Line Items]
Revenues									$ 8,300,000	$ 4,600,000
Accounting Standards Update 2016-02 \| Scenario, Forecast \| Subsequent Event
Revenue from External Customer [Line Items]
Operating lease, right-of-use asset												$ 700,000
Operating lease, liability												$ 700,000
Tax Year 2017
Revenue from External Customer [Line Items]
Additions to tax positions of prior years									168,000
Tax Year 2016
Revenue from External Customer [Line Items]
Additions to tax positions of prior years									149,000
Tax Year 2015
Revenue from External Customer [Line Items]
Additions to tax positions of prior years									$ 230,000

Property and Equipment

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property and Equipment

Property and equipment consists of the following at December 31, 2018 and 2017 (in thousands):


	Useful Lives (Years)	2018		2017
Land	—	$	1,290	$	1,290
Building	39	6,116		6,116
Leasehold improvements	39	808		808
Office equipment and furniture	5	1,492		1,490
Software	5	573		573
Machinery and equipment	7	3,275		3,133
Vehicles	3	6,270		5,516
Construction in Progress	—	8,319		—
Total		28,143		18,926
Less accumulated depreciation		(11,556)		(11,274)
Total		$	16,587	$	7,652

Depreciation expense for property and equipment was $1.1 million, $1.2 million and $1.4 million for the year ended December 31, 2018, 2017 and 2016, respectively.

In 2017, the Midland fabrication facility suffered damages two separate times, due to hailstorms. We did not incur a loss, as our insurance proceeds fully covered the estimated cost for the repairs. In accordance with ASC 605-40, we reduced the value of the building for these damages.

Deferred Compensation Plans	12 Months Ended
Deferred Compensation Plans	Dec. 31, 2018
Compensation Related Costs [Abstract]
Deferred Compensation Plans	Deferred Compensation Plans Effective January 1, 2016, the Company established a non-qualified deferred compensation plan for executive officers, directors and certain eligible employees. The assets of the deferred compensation plan are held in a rabbi trust and are subject to additional risk of loss in the event of bankruptcy or insolvency of the Company. The plan allows for deferral up to 90% of a participant’s base salary, bonus, commissions, director fees and restricted stock awards. A Company owned life insurance policy held in a rabbi trust is utilized as a source of funding for the plan. The cash surrender value of the life insurance policy is $1.0 million and $894,000 as of December 31, 2018 and 2017, respectively, with a loss related to the policy of $153,900 and a gain of $66,400 reported in other income in our consolidated income statement for the year ended December 31, 2018 and 2017, respectively. For deferrals of base salary, bonus, commissions and director fees, settlement payments are made to participants in cash, either in a lump sum or in periodic installments. The deferred obligation to pay the deferred compensation and the deferred director fees is adjusted to reflect the positive or negative performance of investment measurement options selected by each participant and was $1.1 million and $866,000 as of December 31, 2018 and 2017, respectively. The deferred obligation is included in other long-term liabilities in the consolidated balance sheet. For deferrals of restricted stock units, the plan does not allow for diversification, therefore, distributions are paid in shares of common stock and the obligation is carried at grant value. As of December 31, 2018, 101,895 unvested restricted stock units have been deferred of which 34,732 units have been released and issued to the deferred compensation plan with a value of $871,300.

Commitments and Contingencies (Future Lease Payments) (Details) $ in Thousands	Dec. 31, 2018 USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019	$ 298
2020	118
2021	97
2022	44
2023	35
Thereafter	15
Total	$ 607

Income Taxes (Income Tax Reconciliation) (Details)	12 Months Ended
Income Taxes (Income Tax Reconciliation) (Details)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Statutory rate	21.00%	34.00%	34.00%
State and local taxes	1.50%	1.50%	1.60%
Uncertain tax position	72.90%	0.00%	0.00%
Research and development credit	(48.30%)	0.00%	(7.50%)
Stock based compensation	(5.20%)	(13.40%)	0.30%
Nondeductible compensation	4.10%
Domestic production credit	0.00%	(14.30%)	(5.40%)
Other	(2.70%)	(1.50%)	0.60%
Effective rate	43.30%	6.30%	23.60%
Deferred re-measurement for rate change	0.00%	(1144.40%)	0.00%
Effective rate	43.30%	(1138.10%)	23.60%

Summary of Significant Accounting Policies (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									$ 36,806	$ 40,065	$ 37,637
Add: non-ASC 606 rental revenue									28,672	27,628	34,017
Total revenue	$ 16,160	$ 16,396	$ 18,204	$ 14,718	$ 16,660	$ 15,913	$ 16,218	$ 18,902	65,478	67,693	71,654
Compressor - sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									10,994	13,382	10,038
Flares - sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									2,535	2,755	1,183
Other (Parts/Rebuilds) - sales
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									2,740	4,071	2,400
Service and maintenance
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									$ 20,537	$ 19,857	$ 24,016

Related Party (Narrative) (Details) - Corporate Joint Venture - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Related Party Transaction [Line Items]
Purchases from joint venture	$ 1,000
N-G, LLC
Related Party Transaction [Line Items]
Percent ownership		50.00%
Genis Holdings, LLC \| N-G, LLC
Related Party Transaction [Line Items]
Percent ownership		50.00%
Prepaid Purchases From Joint Venture
Related Party Transaction [Line Items]
Amount prepaid on purchases from joint venture	$ 500

Quarterly Financial Data - Unaudited (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Data [Abstract]

Quarterly Financial Data


2018	Q1		Q2		Q3		Q4		Total
Total revenue	$	14,718	$	18,204	$	16,396	$	16,160	$	65,478
Operating income (loss)	350		226		(44)		106		638
Net income (loss)	225		247		236		(282)		426
Net income (loss) per share - Basic	0.02		0.02		0.02		(0.02)		0.03
Net income (loss) per share - Diluted	0.02		0.02		0.02		(0.02)		0.03


2017	Q1		Q2		Q3		Q4		Total
Total revenue	$	18,902	$	16,218	$	15,913	$	16,660	$	67,693
Operating income	343		414		593		217		1,567
Net income ⁽¹⁾	252		375		522		18,702		19,851
Net income per share - Basic	0.02		0.03		0.04		1.46		1.55
Net income per share - Diluted	0.02		0.03		0.04		1.42		1.51

(1) The increase in fourth quarter net income is largely a result of the 2017 Tax Act, see Note 7.

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 426	$ 19,851	$ 6,469
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	22,049	21,302	21,796
Deferred taxes	(5)	(21,582)	(2,713)
Gain on disposal of assets	(69)	(87)	(86)
Loss on retirement of rental equipment	0	0	545
Bad debt allowance	(185)	90	61
Inventory allowance	0	273	566
Stock based compensation	2,385	4,038	2,299
(Loss) Gain on company owned life insurance	154	(67)	(14)
Changes in assets (increase) decrease in:
Trade accounts receivables	1,500	(1,246)	1,668
Inventory	(5,757)	(5,350)	1,131
Prepaid income taxes and prepaid expenses	(1,318)	(1,806)	(1,539)
Changes in liabilities increase (decrease) in:
Accounts payable and accrued liabilities	3,597	3,410	(439)
Deferred income	(104)	(2,040)	1,954
Other	741	666	159
Tax benefit from equity compensation	0	0	(72)
NET CASH PROVIDED BY OPERATING ACTIVITIES	23,414	17,452	31,785
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of rental, property and equipment	(39,790)	(13,489)	(3,321)
Purchase of company owned life insurance	(289)	(620)	(194)
Proceeds from insurance claim	0	1,231	0
Proceeds from sale of property and equipment	69	87	101
NET CASH USED IN INVESTING ACTIVITIES	(40,010)	(12,791)	(3,414)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds of other long-term liabilities	(35)	(23)	(14)
Proceeds from exercise of stock options	680	1,120	1,042
Tax Benefit from equity compensation	0	0	72
Taxes paid related to net share settlement of equity awards	(629)	(644)	(909)
NET CASH PROVIDED BY FINANCING ACTIVITIES	16	453	191
NET CHANGE IN CASH AND CASH EQUIVALENTS	(16,580)	5,114	28,562
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	69,208	64,094	35,532
CASH AND CASH EQUIVALENTS AT END OF PERIOD	52,628	69,208	64,094
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Interest paid	14	14	8
Income taxes paid	85	3,725	5,825
NON-CASH TRANSACTIONS
Transfer of rental equipment to inventory	$ 144	$ 55	$ 724

Deferred Compensation Plans (Details) - USD ($)	12 Months Ended
Deferred Compensation Plans (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation arrangement with individual, cash awards granted, percentage	90.00%
Cash surrender value of life insurance	$ 1,000,000.0	$ 894,000
Gain on company owned life insurance	$ (154,000)	67,000	$ 14,000
Deferred compensation arrangement, deferred shares, released and issued (in shares)	34,732
Deferred compensation arrangement, deferred shares, released and issued, value	$ 871,300
Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation arrangement, deferred shares (in shares)	101,895
Other noncurrent liabilities
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability, current and noncurrent	$ 1,100,000	866,000
Other income
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Gain on company owned life insurance	$ (153,900)	$ 66,400

Summary of Significant Accounting Policies (Concentration Risk) (Details) - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Oxy \| Sales and Rental Income
Concentration Risk [Line Items]
Concentration risk, percentage	28.00%	20.00%	19.00%
Oxy \| Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage	26.00%	14.00%
Devon \| Sales and Rental Income
Concentration Risk [Line Items]
Concentration risk, percentage		15.00%	21.00%

Income Taxes (Components of Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current provision:
Federal	$ (164)	$ 3,074	$ 4,280
State	(84)	260	429
Total current (benefit) provision	(248)	3,334	4,709
Deferred provision:
Federal expense (benefit)	573	(21,582)	(2,713)
Total deferred expense (benefit)	573	(21,582)	(2,713)
Total income tax expense (benefit)	$ 325	$ (18,248)	$ 1,996

Summary of Significant Accounting Policies (Per Share Data) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income	$ (282)	$ 236	$ 247	$ 225	$ 18,702	$ 522	$ 375	$ 252	$ 426	$ 19,851	$ 6,469
Denominator:
Weighted average common shares outstanding, Basic (in shares)									12,965,000	12,831,000	12,702,000
Dilutive effect of stock options and restricted shares (in shares)									268,000	279,000	233,000
Weighted average common shares outstanding, Diluted (in shares)									13,233,000	13,110,000	12,935,000
Earnings per common share:
Earnings per share - Basic (in dollars per share)	$ (0.02)	$ 0.02	$ 0.02	$ 0.02	$ 1.46	$ 0.04	$ 0.03	$ 0.02	$ 0.03	$ 1.55	$ 0.51
Earnings per share - Diluted (in dollars per share)	$ (0.02)	$ 0.02	$ 0.02	$ 0.02	$ 1.42	$ 0.04	$ 0.03	$ 0.02	$ 0.03	$ 1.51	$ 0.50
Stock Options
Earnings per common share:
Anti-dilutive securities (in shares)									82,167	83,917	51,167
Range of exercise prices, lower limit (in dollars per share)									$ 23.30	$ 28.15	$ 30.41
Range of exercise prices, upper limit (in dollars per share)									$ 33.36	$ 33.36	$ 33.36

Stock-Based Compensation (Restricted Stock Activity) (Details) - Restricted Stock - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Shares
Outstanding, Beginning Balance (in shares)	184,389	139,451	145,588
Granted (in shares)	140,988	126,432	139,451
Vested (in shares)	(110,747)	(81,494)	(145,558)
Canceled/Forfeited (in shares)	0	0	0
Outstanding, Ending Balance (in shares)	214,630	184,389	139,451	145,588
Weighted Average Exercise Price
Outstanding, Beginning Balance (in dollars per share)	$ 25.32	$ 21.34	$ 19.17
Granted (in dollars per share)	24.55	27.06	21.34
Vested (in dollars per share)	23.97	21.20	19.17
Canceled/Forfeited (in dollars per share)	0	0	0
Outstanding, Ending Balance (in dollars per share)	$ 25.51	$ 25.32	$ 21.34	$ 19.17
Weighted Average Remaining Contractual Life (years)
Weighted Average Remaining Contractual Life (years)	8 years 10 months 6 days	8 years 9 months 29 days	9 years 1 month 17 days	9 years 1 month 13 days
Aggregate Intrinsic Value (in thousands)
Aggregate Intrinsic Value, Outstanding	$ 3,529	$ 4,831	$ 4,483	$ 3,246
Aggregate Intrinsic Value, Granted	3,461	3,421	3,007
Aggregate Intrinsic Value, Vested	$ 2,806	$ 2,361	$ 2,963

Retirement of Long-Lived Assets	12 Months Ended
Retirement of Long-Lived Assets	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Retirement of Long-Lived Assets	Retirement of Long-Lived AssetsDuring the annual review of our rental compressor units, management looks for any units that are not of the type, configuration, make or model that our customers are demanding or that were not cost efficient to refurbish, maintain and/or operate. From our review in 2018, we retired 13 units from our rental fleet. We recorded no loss on the retirement, due to the units being completely depreciated at the time of retirement. We had no retirement from our rental fleet in 2017. From our review in 2016, we determined 63 units should be retired from our rental fleet with key components from those units being re-utilized in future unit builds and/or repairs. We performed an optimization review and recorded a $545,000 loss on retirement of rental equipment to reduce the book value of each unit to the estimated fair value of approximately $242,000 for key components being kept.

Rental Activity (Details) - USD ($) $ in Thousands	12 Months Ended
Rental Activity (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property Subject to or Available for Operating Lease [Line Items]
Depreciation	$ 21,875	$ 21,147	$ 21,641
Operating Leases, Future Minimum Payments Receivable [Abstract]
2019	7,245
2020	3,334
2021	2,763
2022	2,644
2023	1,058
Total	$ 17,044
Minimum
Property Subject to or Available for Operating Lease [Line Items]
Rental arrangements, original term	6 months
Maximum
Property Subject to or Available for Operating Lease [Line Items]
Rental arrangements, original term	24 months
Rental Equipment
Property Subject to or Available for Operating Lease [Line Items]
Depreciation	$ 20,900	$ 20,000	$ 20,200

Summary of Significant Accounting Policies (Contract Balances) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Accounts receivable - contracts with customers	$ 4,353	$ 5,454
Accounts receivable - non-ASC 606	3,157	3,649
Total Accounts Receivable	7,510	9,103
Less: Allowance for doubtful accounts	(291)	(569)
Total Accounts Receivable, net	7,219	8,534
Deferred income	81	185
Revenue recognized	$ 176	$ 1,900

Credit Facility	12 Months Ended
Credit Facility	Dec. 31, 2018
Debt Disclosure [Abstract]
Credit Facility	Credit Facility We have a senior secured revolving credit agreement with JP Morgan Chase Bank, N.A (the "Amended Credit Agreement") aggregate commitment of $30 million, subject to collateral availability. We also have a right to request from the Lender, on an uncommitted basis, an increase of up to $20 million on the aggregate commitment (which could potentially increase the commitment amount to $50 million). On August 31, 2017, we amended and renewed the Amended Credit Agreement, which was set to expire on December 31, 2017. The Credit Agreement Amendment extends the maturity date to December 31, 2020. No other material revisions were made to the credit facility. Borrowing Base. At any time before the maturity of the Amended Credit Agreement, we may draw, repay and re-borrow amounts available under the borrowing base up to the maximum aggregate availability discussed above. Generally, the borrowing base equals the sum of (a) 80% of our eligible accounts receivable plus (b) 50% of the book value of our eligible general inventory (not to exceed 50% of the commitment amount at the time) plus (c) 75% of the book value of our eligible equipment inventory. JPMorgan Chase Bank (the “Lender”) may adjust the borrowing base components if material deviations in the collateral are discovered in future audits of the collateral. We had $29.5 million borrowing base availability at December 31, 2018 under the terms of our Amended Credit Agreement. Interest and Fees. Under the terms of the Amended Credit Agreement, we have the option of selecting the applicable variable rate for each revolving loan, or portion thereof, of either (a) LIBOR multiplied by the Statutory Reserve Rate (as defined in the Amended Credit Agreement), with respect to this rate, for Eurocurrency funding, plus the Applicable Margin (“LIBOR-based”), or (b) CB Floating Rate, which is the Lender's Prime Rate less the Applicable Margin; provided, however, that no more than three LIBOR-based borrowings under the agreement may be outstanding at any one time. For purposes of the LIBOR-based interest rate, the Applicable Margin is 1.50%. For purposes of the CB Floating Rate, the Applicable Margin is 1.25%. Accrued interest is payable monthly on outstanding principal amounts, provided that accrued interest on LIBOR-based loans is payable at the end of each interest period, but in no event less frequently than quarterly. In addition, fees and expenses are payable in connection with our requests for letters of credit (generally equal to the Applicable Margin for LIBOR-related borrowings multiplied by the face amount of the requested letter of credit) and administrative and legal costs. Maturity . The maturity date of the Amended Credit Agreement is December 31, 2020, at which time all amounts borrowed under the agreement will be due and outstanding letters of credit must be cash collateralized. The agreement may be terminated early upon our request or the occurrence of an event of default. Security. The obligations under the Amended Credit Agreement are secured by a first priority lien on all of our inventory and accounts and lease receivables, along with a first priority lien on a variable number of our leased compressor equipment the book value of must be maintained at a minimum of 2.00 to 1.00 commitment coverage ratio (such ratio being equal to (i) the amount of the borrowing base as of such date to (ii) the amount of the commitment as of such date.) Covenants. The Amended Credit Agreement contains customary representations and warranties, as well as covenants which, among other things, limit our ability to incur additional indebtedness and liens; enter into transactions with affiliates; make acquisitions in excess of certain amounts; pay dividends; redeem or repurchase capital stock or senior notes; make investments or loans; make negative pledges; consolidate, merge or effect asset sales; or change the nature of our business. In addition, we also have certain financial covenants that require us to maintain a leverage ratio less than or equal to 2.50 to 1.00 as of the last day of each fiscal quarter. Events of Default and Acceleration. The Amended Credit Agreement contains customary events of default for credit facilities of this size and type, and includes, without limitation, payment defaults; defaults in performance of covenants or other agreements contained in the loan documents; inaccuracies in representations and warranties; certain defaults, termination events or similar events; certain defaults with respect to any other Company indebtedness in excess of $50,000; certain bankruptcy or insolvency events; the rendering of certain judgments in excess of $150,000; certain ERISA events; certain change in control events and the defectiveness of any liens under the secured revolving credit facility. Obligations under the Amended Credit Agreement may be accelerated upon the occurrence of an event of default. As of December 31, 2018, we were in compliance with all covenants in our Amended Credit Agreement. A default under our Credit Agreement could trigger the acceleration of our bank debt so that it is immediately due and payable. Such default would likely limit our ability to access other credit. At December 31, 2018 our balance on the line of credit was $417,000. Our weighted average interest rate for the year ended December 31, 2018 was 3.81%.

Income Taxes Income Taxes (Narrative) (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Income Tax Disclosure [Abstract]
Tax Cuts and Jobs Act, change in tax rate, income tax expense (benefit)		$ (18,400)
Net operating loss carryforward	$ 10,700	10,700
Income Tax Contingency [Line Items]
Additions to tax positions of prior years	547	547
Income tax penalties and interest accrued	$ 55	55
Tax Year 2017
Income Tax Contingency [Line Items]
Additions to tax positions of prior years		168
Tax Year 2016
Income Tax Contingency [Line Items]
Additions to tax positions of prior years		149
Tax Year 2015
Income Tax Contingency [Line Items]
Additions to tax positions of prior years		$ 230