Natural Gas Services (NGS) 10-K 9 Mar 18 2017 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2017	Mar. 02, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	NATURAL GAS SERVICES GROUP INC
Entity Central Index Key	1,084,991
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		12,982,262
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 321,493,471

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 69,208	$ 64,094
Trade accounts receivable, net of allowance for doubtful accounts of $569 and $597, respectively	8,534	7,378
Inventory	26,224	21,433
Prepaid income taxes	3,443	1,482
Prepaid expenses and other	817	972
Total current assets	108,226	95,359
Long-Term Inventory, net of allowance for obsolescence of $15 and $15, respectively	2,829	2,488
Rental equipment, net of accumulated depreciation of $145,851 and $126,096, respectively	167,099	175,972
Property and equipment, net of accumulated depreciation of $11,274 and $11,267, respectively	7,652	7,753
Goodwill	10,039	10,039
Intangibles, net of accumulated amortization of $1,632 and $1,508, respectively	1,526	1,651
Other assets	939	262
Total assets	298,310	293,524
Current Liabilities:
Line of credit	0	417
Accounts payable	4,162	971
Accrued liabilities	3,106	2,887
Deferred income	185	2,225
Total current liabilities	7,453	6,500
Line of credit	417	0
Deferred income tax liability	32,163	53,745
Other long-term liabilities	958	325
Total liabilities	40,991	60,570
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; 12,880 and 12,764 shares issued and outstanding, respectively	129	128
Additional paid-in capital	105,325	100,812
Retained earnings	151,865	132,014
Total stockholders' equity	257,319	232,954
Total liabilities and stockholders' equity	$ 298,310	$ 293,524

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Assets:
Allowance for doubtful accounts	$ 569	$ 597
Allowance for inventory obsolescence	15	15
Assets, Noncurrent [Abstract]
Accumulated depreciation, rental equipment	145,851	126,069
Accumulated depreciation, property and equipment	11,274	11,267
Accumulated amortization, intangibles	$ 1,632	$ 1,508
Stockholders' Equity Attributable to Parent [Abstract]
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	30,000,000	30,000,000
Common stock, shares issued	12,880,000	12,764,000
Common stock, shares outstanding	12,880,000	12,764,000

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Rental income	$ 46,046	$ 56,717	$ 76,432
Sales	20,208	13,621	18,519
Service and maintenance income	1,439	1,316	968
Total revenue	67,693	71,654	95,919
Operating costs and expenses:
Cost of rentals, exclusive of depreciation stated separately below	18,087	20,350	28,750
Cost of sales, exclusive of depreciation stated separately below	16,286	11,124	13,633
Cost of service and maintenance, exclusive of depreciation stated separately below	370	398	272
Loss on retirement of rental equipment	0	545	4,370
Selling, general, and administrative expenses	10,081	9,011	10,989
Depreciation and amortization	21,302	21,796	22,758
Total operating costs and expenses	66,126	63,224	80,772
Operating income	1,567	8,430	15,147
Other income (expense):
Interest expense	(14)	(8)	(15)
Other income	50	43	132
Total other income, net	36	35	117
Income before provision for income taxes	1,603	8,465	15,264
Provision for income taxes:
Current	3,334	4,709	6,963
Deferred	(21,582)	(2,713)	(1,846)
Total income tax expense (benefit)	(18,248)	1,996	5,117
Net income	$ 19,851	$ 6,469	$ 10,147
Earnings per share:
Earnings per share - Basic (in dollars per share)	$ 1.55	$ 0.51	$ 0.81
Earnings per share - Diluted (in dollars per share)	$ 1.51	$ 0.50	$ 0.79
Weighted average shares outstanding:
Weighted average shares outstanding, Basic (in shares)	12,831	12,702	12,567
Weighted average shares outstanding, Diluted (in shares)	13,110	12,935	12,793

Consolidated Statements of Stoc

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 at Dec. 31, 2014		0
Common stock, shares outstanding, beginning of period at Dec. 31, 2014			12,466,000
Balance, beginning of period at Dec. 31, 2014	$ 210,587	$ 0	$ 124	$ 95,065	$ 115,398
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options, shares			66,000
Exercise of common stock options	776		$ 1	775
Compensation expense on common stock options	601			601
Issuance of restricted stock, shares			71,000
Issuance of restricted stock	0
Tax benefit (expense) of equity compensation	(379)			(379)
Compensation expense on restricted common stock	2,944		$ 1	2,943
Taxes paid related to net shares settlement of equity awards	(695)			(695)
Net income	10,147				10,147
Common stock, shares outstanding, end of period at Dec. 31, 2015			12,603,000
Balance, end of period at Dec. 31, 2015	223,981		$ 126	98,310	125,545
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options, 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			99,000
Issuance of restricted stock	0
Tax benefit (expense) 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 at Dec. 31, 2016	0	0
Common stock, shares outstanding, end of period at Dec. 31, 2016	12,764,000		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			56,000
Exercise of common stock options	1,120		$ 0	1,120
Compensation expense on common stock options	363			363
Issuance of restricted stock, 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 at Dec. 31, 2017	0	0
Common stock, shares outstanding, end of period 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

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 19,851	$ 6,469	$ 10,147
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	21,302	21,796	22,758
Deferred taxes	(21,582)	(2,713)	(1,846)
Gain on disposal of assets	(87)	(86)	(179)
Loss on retirement of rental equipment	0	545	4,370
Bad debt allowance	90	61	477
Inventory allowance	273	566	205
Stock based compensation	4,038	2,299	3,545
Gain on company owned life insurance	(67)	(14)	0
Changes in assets (increase) decrease in:
Trade accounts receivables	(1,246)	1,668	824
Inventory	(5,350)	1,131	5,337
Prepaid income taxes and prepaid expenses	(1,806)	(1,539)	5,774
Changes in liabilities increase (decrease) in:
Accounts payable and accrued liabilities	3,410	(439)	(7,220)
Current income tax liability	0	0	(1,230)
Deferred income	(2,040)	1,954	(1,364)
Other	666	159	(32)
Tax benefit from equity compensation	0	(72)	0
NET CASH PROVIDED BY OPERATING ACTIVITIES	17,452	31,785	41,566
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of rental, property and equipment	(13,489)	(3,321)	(12,459)
Purchase of company owned life insurance	(620)	(194)	0
Proceeds from Insurance Settlement, Investing Activities	1,231	0	0
Proceeds from sale of property and equipment	87	101	189
NET CASH USED IN INVESTING ACTIVITIES	(12,791)	(3,414)	(12,270)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payments of other long-term liabilities	(23)	(14)	(26)
Proceeds from exercise of stock options	1,120	1,042	776
Tax benefit from equity compensation	0	72	0
Taxes paid related to net share settlement of equity awards	(644)	(909)	(695)
NET CASH PROVIDED BY FINANCING ACTIVITIES	453	191	55
NET CHANGE IN CASH AND CASH EQUIVALENTS	5,114	28,562	29,351
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	64,094	35,532	6,181
CASH AND CASH EQUIVALENTS AT END OF PERIOD	69,208	64,094	35,532
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Interest paid	14	8	15
Income taxes paid	3,725	5,825	6,530
NON-CASH TRANSACTIONS
Transfer of rental equipment to inventory	55	724	2,309
Transfer of inventory to property and equipment	$ 0	$ 0	$ 1,624

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	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 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. 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 $569,000 and $597,000 at December 31, 2017 and 2016 , respectively. Management believes that the allowance is adequate; however, actual write-offs may exceed the recorded allowance. Revenue Recognition Revenue from the sales of custom and fabricated compressors, and flare systems is recognized when title passes to the customer, the customer assumes risks and rewards of ownership, collectability is reasonably assured and delivery occurs as directed by our customer. Exchange and rebuilt compressor revenue is recognized when both the replacement compressor has been delivered and the rebuild assessment has been completed. Revenue from compressor service and retrofitting services is recognized upon providing services to the customer. Maintenance agreement revenue is recognized as services are rendered. Rental revenue is recognized over the terms of the respective rental agreements. Deferred income represents payments received before a product is shipped. Revenue from the sale of rental units is included in sales revenue when equipment is shipped or title is transferred to the customer. 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. Title of the equipment and risk of loss passes to the customer when the equipment is complete and ready for shipment, per the customer’s agreement. At the transfer of title, all risks of ownership has passed to the customer on the manufactured items that have not yet been shipped. 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 this agreement are consistent with the credit terms on all other sales. All risks of loss are shouldered by the customer, and there are no exceptions to the customer’s commitment to accept and pay for this manufactured equipment. Revenues recognized at the completion of manufacturing in 2017 and 2016 were approximately $4.6 million and $5.6 million , respectively. Major Customers and Concentration of Credit Risk Sales and rental income to Occidental Permian, LTD. ("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, respectively. Sales and rental income to Devon and Oxy in 2015 amounted to 21% and 10% of revenue. No other single customer accounted for more than 10% of our revenues in 2017 , 2016 or 2015 . Oxy amounted to 14% of our accounts receivable as of December 31, 2017. Oxy, APR Energy, LLC and BP America Inc. amounted to 15% , 15% and 14% , respectively, of our accounts receivable as of December 31, 2016. No other customers amounted to more than 10% of our accounts receivable as of December 31, 2017 and 2016 . 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 $15,000 and $15,000 at December 31, 2017 and 2016 , respectively. There were 7 newly completed compressor units at December 31, 2017 and December 31, 2016 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, 2017 and 2016 , inventory consisted of the following (in thousands): 2017 2016 Raw materials -current $ 22,813 $ 15,877 Raw materials - long term 2,829 2,488 Finished Goods 1,022 2,558 Work in process 2,389 2,998 Total $ 29,053 $ 23,921 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 2017 and 2016, we had $6.4 million and $1.9 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 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, 2017 , 2016 and 2015 (in thousands): 2017 2016 2015 Rentals $ 20,861 $ 21,325 $ 22,308 Sales 265 291 281 Service & Maintenance 21 25 16 Total $ 21,147 $ 21,641 $ 22,605 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, 2017, 2016 or 2015. 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. Due to continued low oil and natural gas prices, we determined a triggering event occurred during each quarter and we performed a goodwill impairment test each quarter of 2017 and our annual goodwill impairment test was performed in the fourth quarter of 2017 . We experienced no impairment of goodwill during the years ended December 31, 2017 or 2016 . Intangibles At December 31, 2017 , NGSG had intangible assets, which relate to developed technology and a trade name. The carrying amount net of accumulated amortization at December 31, 2017 and 2016 was $1.5 million and $1.7 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 seven years as of December 31, 2017 . Amortization expense recognized in each of the years ending December 31, 2017 , 2016 , and 2015 was $125,000 . Estimated amortization expense for the years 2018 -2024 is $125,000 per year. NGSG has an intangible asset with a gross carrying value of $654,000 at December 31, 2017 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, 2017 December 31, 2016 Useful Life (years) Gross Carrying Value Accumulated Amortization Net Book Value Gross Carrying Value Accumulated Amortization Net Book Value Developed Technology 20 $ 2,505 $ 1,633 $ 872 $ 2,505 $ 1,508 $ 997 Trade Name Indefinite 654 — 654 654 — 654 Total $ 3,159 $ 1,633 $ 1,526 $ 3,159 $ 1,508 $ 1,651 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, 2017 or 2016 . Separately, we reviewed our indefinite life intangible for impairment with our goodwill impairment review, which we performed each quarter in 2017 due to a continued decline in our rental utilization and then annually in the fourth quarter of 2017. Based on this analysis, we experienced no impairment on our indefinite life intangible during the years ended December 31, 2017 or 2016. 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 $65,000 and $103,000 for December 31, 2017 and 2016 , respectively, and is included in accrued liabilities on the consolidated balance sheet. 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. 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 2017 , 2016 and 2015 . The following table sets forth the computation of basic and diluted earnings per share (in thousands, except per share amounts): Year Ended December 31, 2017 2016 2015 Numerator: Net income $ 19,851 $ 6,469 $ 10,147 Denominator for basic net income per common share: Weighted average common shares outstanding 12,831 12,702 12,567 Denominator for diluted net income per share: Weighted average common shares outstanding 12,831 12,702 12,567 Dilutive effect of stock options and restricted shares 279 233 226 Diluted weighted average shares 13,110 12,935 12,793 Earnings per common share: Basic $ 1.55 $ 0.51 $ 0.81 Diluted $ 1.51 $ 0.50 $ 0.79 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. In the year-ended December 31, 2015, options to purchase 107,500 shares of common stock with exercise prices ranging from $22.90 to $33.36 were not included in the computation of dilutive income per share, due to their anti-dilutive effect 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, 2017 or 2016 . 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 makes 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”). As we do not have all of the necessary information to analyze all income tax effects of the 2017 Tax Act, we will continue to evaluate tax reform and adjust the provisional amounts as additional information is obtained. We expect to complete our detailed analysis no later than the fourth quarter of 2018. See Note 7, “Income Taxes,” for further information on the financial statement impact of the 2017 Tax Act. 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, 2017 and 2016 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 No. 2016-02, Leases (Topic 842). Under the new guidance, a lessee will be required to recognize assets and liabilities for capital 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. 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 effective during our first quarter ending March 31, 2019. We are currently determining the impacts of the new standard on our consolidated financial statements and the additional applicable disclosure requirements. On May 28, 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606). This update provides a five-step analysis on how an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance also requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. In August 2015, the FASB issued an accounting standards update for a one-year deferral of the revenue recognition standard’s effective date for all entities, which changed the effectiveness to interim and annual reporting periods beginning after December 15, 2017. As a result, we adopted the guidance on January 1, 2018. The guidance offered two transition methods: a full retrospective approach to be applied to each prior reporting period presented or a modified retrospective approach where the cumulative effect of initially applying the standard is recognized at the date of initial application. We have selected the modified retrospective transition method. We have determined the impact of the new standard on our consolidated financial statements. Our approach included performing a detailed review of key contracts that are representative of our various revenue streams and comparing our historical accounting policies and practices to the new standard. Based upon our analysis, we have determined there will be no material financial impact upon adoption, but we will have a change in our disclosures under the new standard and have implemented new internal controls to ensure compliance under this new standard. Reclassification of Prior Period Balances Certain reclassifications have been made to prior period amounts to conform to the current-year presentation. These reclassifications had no effect on the reported results of operations.

Rental Activity

Rental Activity	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Rental Activity	Rental Activity We 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 $20.0 million , $20.2 million and $21.0 million for the years ended December 31, 2017, 2016 and 2015, respectively. Future minimum rent payments for arrangements not on a month-to-month basis at December 31, 2017 are as follows : Years Ending December 31, (in thousands) 2018 $ 6,494 2019 976 2020 543 2021 542 2022 542 Total $ 9,097

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and Equipment	Property and Equipment Property and equipment consists of the following at December 31, 2017 and 2016 (in thousands): Useful Lives (Years) 2017 2016 Land — $ 1,290 $ 169 Building 39 6,116 6,856 Leasehold improvements 39 808 794 Office equipment and furniture 5 1,490 1,454 Software 5 573 573 Machinery and equipment 7 3,133 3,111 Vehicles 3 5,516 6,063 Total 18,926 19,020 Less accumulated depreciation (11,274 ) (11,267 ) Total $ 7,652 $ 7,753 Depreciation expense for property and equipment was $1.2 million , $1.4 million and $1.6 million for the year ended December 31, 2017, 2016 and 2015 , respectively. In 2017, the Midland fabrication facility suffered two separate damages, due to hailstorms. We did not incur a loss, as our insurance proceed fully cover the estimated cost for the repair. In accordance with ASC 605-40, we reduced the value of the building for these damages.

Retirement of Long-Lived Assets

Retirement of Long-Lived Assets	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Retirement of Long-Lived Assets	Retirement of Long-Lived Assets During 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. 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. As a result of our 2015 review, we retired 258 units from our rental fleet with key components from those units being re-utilized in future unit builds and/or repairs. Based on our optimization review we recorded a $4.4 million loss on the retirement of rental equipment to reduce the book value of each unit to the estimated fair value of approximately $967,000 for the key components being kept. These retirements are recorded in the consolidated income statement under loss on retirement of rental equipment.

Deferred Compensation Plans

Deferred Compensation Plans	12 Months Ended
	Dec. 31, 2017
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 $894,000 and $207,000 as of December 31, 2017 and 2016, respectively, with a gain related to the policy of $66,400 and $13,900 reported in other income in our consolidated income statement for the year ended December 31, 2017 and 2016, 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 $866,000 and $208,000 as of December 31, 2017 and 2016, respectively. The deferred obligation is included in other long-term liabilities in the consolidated balance sheet. For deferrals of restricted stock, the plan does not allow for diversification, therefore, distributions are paid in shares and the obligation is carried at grant value. As of December 31, 2017 , a total of $97,011 unvested restricted stock units have been deferred.

Credit Facility

Credit Facility	12 Months Ended
	Dec. 31, 2017
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, 2017 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, 2017 , 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, 2017 our balance on the line of credit was $417,000 . Our weighted average interest rate for the year ended December 31, 2017 was 1.60% .

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The provision for income taxes for the years ended December 31, 2017 , 2016 and 2015 , consists of the following (in thousands): 2017 2016 2015 Current provision: Federal $ 3,074 $ 4,280 $ 6,440 State 260 429 523 Total current provision 3,334 4,709 6,963 Deferred provision: Federal benefit (21,582 ) (2,713 ) (1,846 ) Total deferred benefit (21,582 ) (2,713 ) (1,846 ) Total (benefit) provision $ (18,248 ) $ 1,996 $ 5,117 On December 22, 2017, the U.S. government enacted the 2017 Tax Act. The 2017 Tax Act makes broad and complex changes to the U.S. tax code that affects the Company’s 2017 financial results. The 2017 Tax Act also establishes 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 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. As we do not have all of the necessary information to analyze all income tax effects of the 2017 Tax Act, we will continue to evaluate tax reform and adjust the provisional amounts as additional information is obtained. We expect to complete our detailed analysis no later than the fourth quarter of 2018. The income tax effects of temporary differences that give rise to significant portions of deferred income tax assets and (liabilities) as of December 31, 2017 and 2016 , are as follows (in thousands): 2017 2016 Deferred income tax assets: Stock Compensation $ 843 $ 664 Other 201 84 Total deferred income tax assets $ 1,044 $ 748 Deferred income tax liabilities: Property and equipment $ (32,377 ) (53,120 ) Goodwill and other intangible assets (604 ) (973 ) Other (226 ) (400 ) Total deferred income tax liabilities (33,207 ) (54,493 ) Net deferred income tax liabilities $ (32,163 ) $ (53,745 ) The effective tax rate for the years ended December 31, 2017 , 2016 and 2015 , differs from the statutory rate as follows: 2017 2016 2015 Statutory rate 34.0 % 34.0 % 34.0 % State and local taxes 1.5 % 1.6 % 1.5 % Domestic production credit (14.3 )% (5.4 )% (3.6 )% Permanent stock differences (13.4 )% 0.3 % 1.1 % Other (1.5 )% (6.9 )% 0.5 % Effective rate prior to tax act 6.3 % 23.6 % 33.5 % Deferred re-measurement for rate change (1,144.4 )% — % — % Effective rate (1,138.1 )% 23.6 % 33.5 % Our policy regarding income tax interest and penalties is to expense those items as general and administrative expense. During the years ended December 31, 2017 , 2016 and 2015 , there were no significant income tax interest or penalty items in the statement of income. 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 2013.

Other Long-term Liabilities

Other Long-term Liabilities	12 Months Ended
	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Other Long-term Liabilities	Other Long-term Liabilities We 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 $92,000 and $115,000 as of December 31, 2017 and 2016 , respectively.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
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, 2017 and 2016 , there were no issued or outstanding preferred shares.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	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 2016 performance, Mr. Taylor, was awarded 70,464 restricted shares/units on February 14, 2017, which vest over three years, in equal installments beginning February 14, 2018. On March 23, 2017, 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 23, 2018. We also awarded and issued 15,968 shares of restricted common stock/units to our Board of Directors as partial payment for 2017 directors' fees. The restricted stock/units issued to our directors vests over one year , in quarterly installments, beginning March 31, 2018. Compensation expense related to the restricted shares/units was approximately $3,675,000 , $1,793,000 and $2,944,000 for the years ended December 31, 2017 , 2016, and 2015, respectively. As of December 31, 2017 , there was a total of approximately $1,385,000 of unrecognized compensation expense related to the nonvested portion of these restricted shares/units. This expense is expected to be recognized over the next one year and a quarter. As of December 31, 2017, 162,770 shares were still available for issuance under the Plan. A summary of all restricted stock/units activity as of December 31, 2015, 2016 and 2017 and changes during the years then ended are presented below. Number Weighted Average Weighted Aggregate (in thousands) Outstanding, December 31, 2014 99,238 $ 28.22 9.00 $ 2,286 Granted 145,558 $ 19.17 — $ 2,886 Vested (99,238 ) $ 28.22 — $ 2,100 Canceled/Forfeited — $ — — $ — 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 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 ot 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, 2017 , 313,169 shares were still available for issue under the Stock Option Plan. 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 years ended December 31, are as follows: 2017 2015 Risk free rate 2.12 % 1.56 % Expected life 6 years 6 years Expected volatility 39.59 % 45.07 % Expected dividend yield — — There were no stock option grants made in 2016. A summary of all option activity as of December 31, 2015, 2016 and 2017 and changes during the years then ended are presented below: Number Weighted Average Weighted Aggregate (in thousands) Outstanding, December 31, 2014 432,269 $ 17.55 4.89 $ 2,786 Granted 50,000 $ 22.90 Exercised (66,000 ) $ 11.76 481 Canceled/Forfeited (1,500 ) $ 30.41 $ — 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 Exercisable, December 31, 2017 278,689 $ 19.12 3.54 $ 2,203 The weighted average grant date fair value of options granted during the years 2017 and 2015 was $11.93 and $10.33 , respectively. 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, 2017 , 2016 , and 2015 was approximately $446,000 , $625,000 , and $481,000 respectively. Cash received from stock options exercised during the years ended December 31, 2017 , 2016 , and 2015 was approximately $1,120,000 , $1,042,000 , and $776,000 , respectively. The following table summarizes information about our stock options outstanding at December 31,: 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 65,852 1.56 $ 9.82 65,852 $ 9.82 $15.71-17.81 72,750 1.79 $ 17.53 72,750 $ 17.53 $17.82-20.48 56,750 3.54 $ 19.36 56,750 $ 19.36 $20.49-33.36 131,918 7.34 $ 27.23 83,337 $ 27.70 327,270 4.28 $ 20.21 278,689 $ 19.12 The summary of the status of our unvested stock options as of December 31, 2017 and changes during the year then ended is presented below. Unvested stock options: Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2016 50,833 $ 12.67 Granted 32,750 $ 11.93 Vested (35,002 ) $ 13.73 Unvested at December 31, 2017 48,581 $ 11.41 We recognized stock compensation expense from stock options vesting of $363,000 , $506,000 , and $601,000 for the years ended December 31, 2017 , 2016 and 2015 , respectively. As of December 31, 2017 , there was approximately $282,000 of total unamortized compensation cost related to unvested stock options. We expect to recognize such cost over a weighted-average period of 2.0 years .

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	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 $301,000 , $295,000 , and $387,000 to the 401(k) Plan in 2017 , 2016 and 2015 , 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) 2018 $ 484 2019 122 2020 9 2021 1 Total $ 616 Rent expense under such leases was $ 310,000 , $325,000 , and $375,000 for the years ended December 31, 2017 , 2016 and 2015 , 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.

Quarterly Financial Data

Quarterly Financial Data	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Quarterly Financial Data	Quarterly Financial Data (in thousands, except per share data) – Unaudited 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. 2016 Q1 Q2 Q3 Q4 Total Total revenue $ 21,576 $ 17,194 $ 16,181 $ 16,703 $ 71,654 Operating income 3,767 1,873 1,823 967 8,430 Net income 2,541 1,259 1,509 1,160 6,469 Net income per share - Basic 0.20 0.10 0.12 0.09 0.51 Net income per share - Diluted 0.20 0.10 0.12 0.09 0.50 Amounts may not add due to rounding differences.

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Organization and Principles of Consolidation	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	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	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. It is at least reasonably possible these estimates could be revised in the near term and the revisions could be material.
Cash Equivalents	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	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 $569,000 and $597,000 at December 31, 2017 and 2016 , respectively. Management believes that the allowance is adequate; however, actual write-offs may exceed the recorded allowance.
Revenue Recognition	Revenue Recognition Revenue from the sales of custom and fabricated compressors, and flare systems is recognized when title passes to the customer, the customer assumes risks and rewards of ownership, collectability is reasonably assured and delivery occurs as directed by our customer. Exchange and rebuilt compressor revenue is recognized when both the replacement compressor has been delivered and the rebuild assessment has been completed. Revenue from compressor service and retrofitting services is recognized upon providing services to the customer. Maintenance agreement revenue is recognized as services are rendered. Rental revenue is recognized over the terms of the respective rental agreements. Deferred income represents payments received before a product is shipped. Revenue from the sale of rental units is included in sales revenue when equipment is shipped or title is transferred to the customer. 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. Title of the equipment and risk of loss passes to the customer when the equipment is complete and ready for shipment, per the customer’s agreement. At the transfer of title, all risks of ownership has passed to the customer on the manufactured items that have not yet been shipped. 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 this agreement are consistent with the credit terms on all other sales. All risks of loss are shouldered by the customer, and there are no exceptions to the customer’s commitment to accept and pay for this manufactured equipment.
Major Customers and Concentration of Credit Risk	Major Customers and Concentration of Credit Risk Sales and rental income to Occidental Permian, LTD. ("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, respectively. Sales and rental income to Devon and Oxy in 2015 amounted to 21% and 10% of revenue. No other single customer accounted for more than 10% of our revenues in 2017 , 2016 or 2015 . Oxy amounted to 14% of our accounts receivable as of December 31, 2017. Oxy, APR Energy, LLC and BP America Inc. amounted to 15% , 15% and 14% , respectively, of our accounts receivable as of December 31, 2016. No other customers amounted to more than 10% of our accounts receivable as of December 31, 2017 and 2016 .
Inventory	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.
Rental Equipment and Property and Equipment	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 2017 and 2016, we had $6.4 million and $1.9 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, 2017, 2016 or 2015. 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 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. Due to continued low oil and natural gas prices, we determined a triggering event occurred during each quarter and we performed a goodwill impairment test each quarter of 2017 and our annual goodwill impairment test was performed in the fourth quarter of 2017 .
Intangibles	Intangibles At December 31, 2017 , NGSG had intangible assets, which relate to developed technology and a trade name. The carrying amount net of accumulated amortization at December 31, 2017 and 2016 was $1.5 million and $1.7 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 seven years as of December 31, 2017 . Amortization expense recognized in each of the years ending December 31, 2017 , 2016 , and 2015 was $125,000 . Estimated amortization expense for the years 2018 -2024 is $125,000 per year. NGSG has an intangible asset with a gross carrying value of $654,000 at December 31, 2017 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, 2017 December 31, 2016 Useful Life (years) Gross Carrying Value Accumulated Amortization Net Book Value Gross Carrying Value Accumulated Amortization Net Book Value Developed Technology 20 $ 2,505 $ 1,633 $ 872 $ 2,505 $ 1,508 $ 997 Trade Name Indefinite 654 — 654 654 — 654 Total $ 3,159 $ 1,633 $ 1,526 $ 3,159 $ 1,508 $ 1,651 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, 2017 or 2016 . Separately, we reviewed our indefinite life intangible for impairment with our goodwill impairment review, which we performed each quarter in 2017 due to a continued decline in our rental utilization and then annually in the fourth quarter of 2017. Based on this analysis, we experienced no impairment on our indefinite life intangible during the years ended December 31, 2017 or 2016.
Warranty	Warranty We 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	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.
Per Share Data	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.
Income Taxes	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, 2017 or 2016 . 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 makes 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”).
Fair Value Measurement	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, 2017 and 2016 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	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	Recently Issued Accounting Pronouncements On February 25, 2016, the Financial Accounting Standards Board ("FASB") issued ASU No. 2016-02, Leases (Topic 842). Under the new guidance, a lessee will be required to recognize assets and liabilities for capital 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. 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 effective during our first quarter ending March 31, 2019. We are currently determining the impacts of the new standard on our consolidated financial statements and the additional applicable disclosure requirements. On May 28, 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606). This update provides a five-step analysis on how an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. This guidance also requires more detailed disclosures to enable users of financial statements to understand the nature, amount, timing and uncertainty of revenue and cash flows arising from contracts with customers. In August 2015, the FASB issued an accounting standards update for a one-year deferral of the revenue recognition standard’s effective date for all entities, which changed the effectiveness to interim and annual reporting periods beginning after December 15, 2017. As a result, we adopted the guidance on January 1, 2018. The guidance offered two transition methods: a full retrospective approach to be applied to each prior reporting period presented or a modified retrospective approach where the cumulative effect of initially applying the standard is recognized at the date of initial application. We have selected the modified retrospective transition method. We have determined the impact of the new standard on our consolidated financial statements. Our approach included performing a detailed review of key contracts that are representative of our various revenue streams and comparing our historical accounting policies and practices to the new standard. Based upon our analysis, we have determined there will be no material financial impact upon adoption, but we will have a change in our disclosures under the new standard and have implemented new internal controls to ensure compliance under this new standard. Reclassification of Prior Period Balances Certain reclassifications have been made to prior period amounts to conform to the current-year presentation. These reclassifications had no effect on the reported results of operations.

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Schedule of Inventory	At December 31, 2017 and 2016 , inventory consisted of the following (in thousands): 2017 2016 Raw materials -current $ 22,813 $ 15,877 Raw materials - long term 2,829 2,488 Finished Goods 1,022 2,558 Work in process 2,389 2,998 Total $ 29,053 $ 23,921
Summary of 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, 2017 , 2016 and 2015 (in thousands): 2017 2016 2015 Rentals $ 20,861 $ 21,325 $ 22,308 Sales 265 291 281 Service & Maintenance 21 25 16 Total $ 21,147 $ 21,641 $ 22,605 Property and equipment consists of the following at December 31, 2017 and 2016 (in thousands): Useful Lives (Years) 2017 2016 Land — $ 1,290 $ 169 Building 39 6,116 6,856 Leasehold improvements 39 808 794 Office equipment and furniture 5 1,490 1,454 Software 5 573 573 Machinery and equipment 7 3,133 3,111 Vehicles 3 5,516 6,063 Total 18,926 19,020 Less accumulated depreciation (11,274 ) (11,267 ) Total $ 7,652 $ 7,753
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, 2017 December 31, 2016 Useful Life (years) Gross Carrying Value Accumulated Amortization Net Book Value Gross Carrying Value Accumulated Amortization Net Book Value Developed Technology 20 $ 2,505 $ 1,633 $ 872 $ 2,505 $ 1,508 $ 997 Trade Name Indefinite 654 — 654 654 — 654 Total $ 3,159 $ 1,633 $ 1,526 $ 3,159 $ 1,508 $ 1,651
Schedule of Identified Indefinite-Lived Intangible Assets	The following table represents the identified intangible assets by major asset class (in thousands): December 31, 2017 December 31, 2016 Useful Life (years) Gross Carrying Value Accumulated Amortization Net Book Value Gross Carrying Value Accumulated Amortization Net Book Value Developed Technology 20 $ 2,505 $ 1,633 $ 872 $ 2,505 $ 1,508 $ 997 Trade Name Indefinite 654 — 654 654 — 654 Total $ 3,159 $ 1,633 $ 1,526 $ 3,159 $ 1,508 $ 1,651
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, 2017 2016 2015 Numerator: Net income $ 19,851 $ 6,469 $ 10,147 Denominator for basic net income per common share: Weighted average common shares outstanding 12,831 12,702 12,567 Denominator for diluted net income per share: Weighted average common shares outstanding 12,831 12,702 12,567 Dilutive effect of stock options and restricted shares 279 233 226 Diluted weighted average shares 13,110 12,935 12,793 Earnings per common share: Basic $ 1.55 $ 0.51 $ 0.81 Diluted $ 1.51 $ 0.50 $ 0.79

Rental Activity (Tables)

Rental Activity (Tables)	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Schedule of Future Minimum Rent Payments	Future minimum rent payments for arrangements not on a month-to-month basis at December 31, 2017 are as follows : Years Ending December 31, (in thousands) 2018 $ 6,494 2019 976 2020 543 2021 542 2022 542 Total $ 9,097 Remaining future minimum rental payments (excluding month to month) due under these leases are as follows: Years Ending December 31, (in thousands) 2018 $ 484 2019 122 2020 9 2021 1 Total $ 616

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Summary of 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, 2017 , 2016 and 2015 (in thousands): 2017 2016 2015 Rentals $ 20,861 $ 21,325 $ 22,308 Sales 265 291 281 Service & Maintenance 21 25 16 Total $ 21,147 $ 21,641 $ 22,605 Property and equipment consists of the following at December 31, 2017 and 2016 (in thousands): Useful Lives (Years) 2017 2016 Land — $ 1,290 $ 169 Building 39 6,116 6,856 Leasehold improvements 39 808 794 Office equipment and furniture 5 1,490 1,454 Software 5 573 573 Machinery and equipment 7 3,133 3,111 Vehicles 3 5,516 6,063 Total 18,926 19,020 Less accumulated depreciation (11,274 ) (11,267 ) Total $ 7,652 $ 7,753

Income Taxes Income Taxes (Tabl

Income Taxes Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for Income Taxes	The provision for income taxes for the years ended December 31, 2017 , 2016 and 2015 , consists of the following (in thousands): 2017 2016 2015 Current provision: Federal $ 3,074 $ 4,280 $ 6,440 State 260 429 523 Total current provision 3,334 4,709 6,963 Deferred provision: Federal benefit (21,582 ) (2,713 ) (1,846 ) Total deferred benefit (21,582 ) (2,713 ) (1,846 ) Total (benefit) provision $ (18,248 ) $ 1,996 $ 5,117
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, 2017 and 2016 , are as follows (in thousands): 2017 2016 Deferred income tax assets: Stock Compensation $ 843 $ 664 Other 201 84 Total deferred income tax assets $ 1,044 $ 748 Deferred income tax liabilities: Property and equipment $ (32,377 ) (53,120 ) Goodwill and other intangible assets (604 ) (973 ) Other (226 ) (400 ) Total deferred income tax liabilities (33,207 ) (54,493 ) Net deferred income tax liabilities $ (32,163 ) $ (53,745 )
Effective Income Tax Rate Reconciliation	The effective tax rate for the years ended December 31, 2017 , 2016 and 2015 , differs from the statutory rate as follows: 2017 2016 2015 Statutory rate 34.0 % 34.0 % 34.0 % State and local taxes 1.5 % 1.6 % 1.5 % Domestic production credit (14.3 )% (5.4 )% (3.6 )% Permanent stock differences (13.4 )% 0.3 % 1.1 % Other (1.5 )% (6.9 )% 0.5 % Effective rate prior to tax act 6.3 % 23.6 % 33.5 % Deferred re-measurement for rate change (1,144.4 )% — % — % Effective rate (1,138.1 )% 23.6 % 33.5 %

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2017
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, 2015, 2016 and 2017 and changes during the years then ended are presented below. Number Weighted Average Weighted Aggregate (in thousands) Outstanding, December 31, 2014 99,238 $ 28.22 9.00 $ 2,286 Granted 145,558 $ 19.17 — $ 2,886 Vested (99,238 ) $ 28.22 — $ 2,100 Canceled/Forfeited — $ — — $ — 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
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 years ended December 31, are as follows: 2017 2015 Risk free rate 2.12 % 1.56 % Expected life 6 years 6 years Expected volatility 39.59 % 45.07 % Expected dividend yield — —
Summary of Option Activity	A summary of all option activity as of December 31, 2015, 2016 and 2017 and changes during the years then ended are presented below: Number Weighted Average Weighted Aggregate (in thousands) Outstanding, December 31, 2014 432,269 $ 17.55 4.89 $ 2,786 Granted 50,000 $ 22.90 Exercised (66,000 ) $ 11.76 481 Canceled/Forfeited (1,500 ) $ 30.41 $ — 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 Exercisable, December 31, 2017 278,689 $ 19.12 3.54 $ 2,203
Summary of Stock Options Outstanding	The following table summarizes information about our stock options outstanding at December 31,: 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 65,852 1.56 $ 9.82 65,852 $ 9.82 $15.71-17.81 72,750 1.79 $ 17.53 72,750 $ 17.53 $17.82-20.48 56,750 3.54 $ 19.36 56,750 $ 19.36 $20.49-33.36 131,918 7.34 $ 27.23 83,337 $ 27.70 327,270 4.28 $ 20.21 278,689 $ 19.12
Summary of the Status of Unvested Stock Options	The summary of the status of our unvested stock options as of December 31, 2017 and changes during the year then ended is presented below. Unvested stock options: Shares Weighted Average Grant Date Fair Value Unvested at December 31, 2016 50,833 $ 12.67 Granted 32,750 $ 11.93 Vested (35,002 ) $ 13.73 Unvested at December 31, 2017 48,581 $ 11.41

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments	Future minimum rent payments for arrangements not on a month-to-month basis at December 31, 2017 are as follows : Years Ending December 31, (in thousands) 2018 $ 6,494 2019 976 2020 543 2021 542 2022 542 Total $ 9,097 Remaining future minimum rental payments (excluding month to month) due under these leases are as follows: Years Ending December 31, (in thousands) 2018 $ 484 2019 122 2020 9 2021 1 Total $ 616

Quarterly Financial Data (Table

Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Quarterly Financial Data	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. 2016 Q1 Q2 Q3 Q4 Total Total revenue $ 21,576 $ 17,194 $ 16,181 $ 16,703 $ 71,654 Operating income 3,767 1,873 1,823 967 8,430 Net income 2,541 1,259 1,509 1,160 6,469 Net income per share - Basic 0.20 0.10 0.12 0.09 0.51 Net income per share - Diluted 0.20 0.10 0.12 0.09 0.50

Summary of Significant Accoun27

Summary of Significant Accounting Policies (Narrative) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Dec. 31, 2017USD ($)segment	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
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	$ 569,000				$ 597,000				$ 569,000	$ 597,000
Revenues recognized	16,660,000	$ 15,913,000	$ 16,218,000	$ 18,902,000	16,703,000	$ 16,181,000	$ 17,194,000	$ 21,576,000	67,693,000	71,654,000	$ 95,919,000
Product warranty reserves	65,000				103,000				65,000	103,000
Uncertain tax positions	$ 0				$ 0				$ 0	0
Number of business segments | segment									1
Bill and Hold Arrangement
Revenue from External Customer [Line Items]
Revenues recognized									$ 4,600,000	$ 5,600,000

Summary of Significant Accoun28

Summary of Significant Accounting Policies (Concentration Risk) (Details) - Customer Concentration Risk	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Oxy | Sales and Rental Income
Concentration Risk [Line Items]
Concentration risk, percentage	20.00%	19.00%	10.00%
Oxy | Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage	14.00%	15.00%
Devon | Sales and Rental Income
Concentration Risk [Line Items]
Concentration risk, percentage	15.00%	21.00%	21.00%
APR Energy LLC | Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage		15.00%
BP America | Accounts Receivable
Concentration Risk [Line Items]
Concentration risk, percentage		14.00%

Summary of Significant Accoun29

Summary of Significant Accounting Policies (Inventory) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)compressor	Dec. 31, 2016USD ($)compressor
Inventory [Line Items]
Inventory valuation reserves, deductions	$ 15	$ 15
Available-for-sale or rental, compressor units | compressor	7	7
Raw materials -current	$ 22,813	$ 15,877
Long-Term Inventory, net of allowance for obsolescence of $15 and $15, respectively	2,829	2,488
Finished Goods	1,022	2,558
Work in process	2,389	2,998
Inventory	29,053	23,921
Rental Equipment [Member]
Inventory [Line Items]
Work in process	$ 6,400	$ 1,900

Summary of Significant Accoun30

Summary of Significant Accounting Policies (Property and Equipment) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation	$ 21,147,000	$ 21,641,000	$ 22,605,000
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	$ 20,861,000	21,325,000	22,308,000
Sales
Property, Plant and Equipment [Line Items]
Depreciation	265,000	291,000	281,000
Service & Maintenance
Property, Plant and Equipment [Line Items]
Depreciation	$ 21,000	$ 25,000	$ 16,000

Summary of Significant Accoun31

Summary of Significant Accounting Policies (Intangibles) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Intangible Assets [Line Items]
Impairment of goodwill	$ 0	$ 0
Intangibles, net of accumulated amortization	1,526,000	1,651,000
Amortization expense	125,000
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2,018	125,000
2,019	125,000
2,020	125,000
2,021	125,000
2,022	125,000
2,023	125,000
2,024	125,000
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Value	3,159,000	3,159,000
Accumulated Amortization	1,633,000	1,508,000
Net Book Value	1,526,000	1,651,000
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	20 years
Intangible assets, weighted average remaining life	7 years
Finite-Lived Intangible Assets, Net [Abstract]
Gross Carrying Value	$ 2,505,000	$ 2,505,000
Accumulated Amortization	1,633,000	1,508,000
Net Book Value	$ 872,000	$ 997,000

Summary of Significant Accoun32

Summary of Significant Accounting Policies (Per Share Data) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net income	$ 18,702	$ 522	$ 375	$ 252	$ 1,160	$ 1,509	$ 1,259	$ 2,541	$ 19,851	$ 6,469	$ 10,147
Denominator for basic net income per common share:
Weighted average common shares outstanding, Basic (in shares)									12,831,000	12,702,000	12,567,000
Denominator for diluted net income per share:
Weighted average common shares outstanding, Basic (in shares)									12,831,000	12,702,000	12,567,000
Dilutive effect of stock options and restricted shares (in shares)									279,000	233,000	226,000
Weighted average common shares outstanding, Diluted (in shares)									13,110,000	12,935,000	12,793,000
Earnings per common share:
Earnings per share - Basic (in dollars per share)	$ 1.46	$ 0.04	$ 0.03	$ 0.02	$ 0.09	$ 0.12	$ 0.10	$ 0.20	$ 1.55	$ 0.51	$ 0.81
Earnings per share - Diluted (in dollars per share)	$ 1.42	$ 0.04	$ 0.03	$ 0.02	$ 0.09	$ 0.12	$ 0.10	$ 0.20	$ 1.51	$ 0.50	$ 0.79
Stock Options
Earnings per common share:
Anti-dilutive securities (in shares)									83,917	51,167	107,500
Range of exercise prices, lower limit (in dollars per share)									$ 28.15	$ 30.41	$ 22.90
Range of exercise prices, upper limit (in dollars per share)									$ 33.36	$ 33.36	$ 33.36

Rental Activity (Details)

Rental Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property Subject to or Available for Operating Lease [Line Items]
Depreciation	$ 21,147	$ 21,641	$ 22,605
2,018	6,494
2,019	976
2,020	543
2,021	542
2,022	542
Total	$ 9,097
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	$ 20,000	$ 20,200	$ 21,000

Property and Equipment (Details

Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 18,926	$ 19,020
Less accumulated depreciation	(11,274)	(11,267)
Property and equipment, net	7,652	7,753
Depreciation	21,147	21,641	$ 22,605
Land
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,290	169
Building
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	39 years
Property and equipment, gross	$ 6,116	6,856
Leasehold improvements
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	39 years
Property and equipment, gross	$ 808	794
Office equipment and furniture
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	5 years
Property and equipment, gross	$ 1,490	1,454
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	$ 3,133	3,111
Vehicles
Property, Plant and Equipment [Line Items]
Useful Lives (Years)	3 years
Property and equipment, gross	$ 5,516	6,063
Property, Plant, and Equipment, Excluding Rental Equipment
Property, Plant and Equipment [Line Items]
Depreciation	$ 1,200	$ 1,400	$ 1,600

Retirement of Long-Lived Asse35

Retirement of Long-Lived Assets (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)compressor	Dec. 31, 2015USD ($)compressor
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Loss on retirement of rental equipment	$ 0	$ 545	$ 4,370
Rental Compressor Unit
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Estimated fair value of long-lived assets		$ 242	$ 967
Rental Compressor Unit
Impaired Assets to be Disposed of by Method Other than Sale [Line Items]
Number of rental compressors that are not of demanded type, configuration, make or model | compressor		63	258
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	$ 4,400

Deferred Compensation Plans (De

Deferred Compensation Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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	$ 894,000	$ 207,000
Gain on company owned life insurance	$ 67,000	14,000	$ 0
Restricted Stock
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation arrangement, deferred shares	97,011
Other noncurrent liabilities
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability, current and noncurrent	$ 866,000	208,000
Other income
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Gain on company owned life insurance	$ 66,400	$ 13,900

Credit Facility (Details)

Credit Facility (Details)	12 Months Ended
	Dec. 31, 2017USD ($)loan	Dec. 31, 2016USD ($)
Line of Credit Facility [Line Items]
Line of credit	$ 0	$ 417,000
Revolving Credit Facility
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	1.60%
Revolving Credit Facility | LIBOR-based Rate
Line of Credit Facility [Line Items]
Variable rate, applicable margin	1.50%
Revolving Credit Facility | CB Floating Rate
Line of Credit Facility [Line Items]
Variable rate, applicable margin	1.25%
Revolving Credit Facility | 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
Revolving Credit Facility | Maximum | LIBOR-based Rate
Line of Credit Facility [Line Items]
Reference rate, number of allowable LIBOR-based borrowings outstanding (in loans) | loan	3
Revolving Credit Facility | Minimum
Line of Credit Facility [Line Items]
Minimum commitment coverage ratio allowed	2

Income Taxes (Components of Pro

Income Taxes (Components of Provision for Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current provision:
Federal	$ 3,074	$ 4,280	$ 6,440
State	260	429	523
Total current provision	3,334	4,709	6,963
Deferred provision:
Federal benefit	(21,582)	(2,713)	(1,846)
Total deferred benefit	(21,582)	(2,713)	(1,846)
Total income tax expense (benefit)	$ (18,248)	$ 1,996	$ 5,117

Income Taxes Income Taxes (2017

Income Taxes Income Taxes (2017 Tax Act) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017USD ($)
Income Tax Disclosure [Abstract]
Tax Cuts and Jobs Act, change in tax rate, income tax expense (benefit)	$ (18.4)

Income Taxes (Components of Def

Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred income tax assets:
Stock Compensation	$ 843	$ 664
Other	201	84
Total deferred income tax assets	1,044	748
Deferred income tax liabilities:
Property and equipment	(32,377)	(53,120)
Goodwill and other intangible assets	(604)	(973)
Other	(226)	(400)
Total deferred income tax liabilities	(33,207)	(54,493)
Net deferred income tax liabilities	$ (32,163)	$ (53,745)

Income Taxes (Income Tax Reconc

Income Taxes (Income Tax Reconciliation) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Statutory rate	34.00%	34.00%	34.00%
State and local taxes	1.50%	1.60%	1.50%
Domestic production credit	(14.30%)	(5.40%)	(3.60%)
Permanent stock differences	(13.40%)
Permanent stock differences		0.30%	1.10%
Other	(1.50%)	(6.90%)	0.50%
Effective rate prior to tax act	6.30%	23.60%	33.50%
Deferred re-measurement for rate change	(1144.40%)	0.00%	0.00%
Effective rate	(1138.10%)	23.60%	33.50%

Other Long-term Liabilities (De

Other Long-term Liabilities (Details) - Paint and Coatings - USD ($) $ in Thousands	Jul. 30, 2008	Dec. 31, 2017	Dec. 31, 2016
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	$ 92	$ 115

Stockholders' Equity (Details)

Stockholders' Equity (Details) - shares	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity Attributable to Parent [Abstract]
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Stock-Based Compensation (Restr

Stock-Based Compensation (Restricted Stock Narrative) (Details) - Restricted Stock - USD ($) $ in Thousands	Mar. 23, 2017	Feb. 14, 2017	Jun. 18, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted				126,432	139,451	145,558
Share-based compensation expense				$ 3,675	$ 1,793	$ 2,944
Total unrecognized compensation expense				$ 1,385
Unrecognized compensation cost related to stock options, weighted average period for recognition				15 months
Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted		70,464
Award vesting period		3 years
Chief Financial Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	20,000
Vice President of Technical Services
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares granted	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]
Shares granted				15,968
Award vesting period				1 year
2009 Restricted Stock/Units Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized			500,000
Number of shares authorized			800,000
Share-based compensation arrangement by share-based payment award, equity instruments other than options, nonvested (in shares)				162,770

Stock-Based Compensation (Res45

Stock-Based Compensation (Restricted Stock Activity) (Details) - Restricted Stock - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of Shares
Outstanding, Beginning Balance (in shares)	139,451	145,588	99,238
Granted (in shares)	126,432	139,451	145,558
Vested (in shares)	(81,494)	(145,558)	(99,238)
Canceled/Forfeited (in shares)	0	0	0
Outstanding, Ending Balance (in shares)	184,389	139,451	145,588	99,238
Weighted Average Exercise Price
Outstanding, Beginning Balance (in dollars per share)	$ 21.34	$ 19.17	$ 28.22
Granted (in dollars per share)	27.06	21.34	19.17
Vested (in dollars per share)	21.20	19.17	28.22
Canceled/Forfeited (in dollars per share)	0	0	0
Outstanding, Ending Balance (in dollars per share)	$ 25.32	$ 21.34	$ 19.17	$ 28.22
Weighted Average Remaining Contractual Life (years)
Weighted Average Remaining Contractual Life (years)	8 years 8 months 60 days	9 years 1 month 18 days	9 years 1 month 12 days	9 years
Aggregate Intrinsic Value (in thousands)
Aggregate Intrinsic Value, Outstanding	$ 4,831	$ 4,483	$ 3,246	$ 2,286
Aggregate Intrinsic Value, Granted	3,421	3,007	2,886
Aggregate Intrinsic Value, Vested	$ 2,361	$ 2,963	$ 2,100

Stock-Based Compensation (Stock

Stock-Based Compensation (Stock Options Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 16, 2016	Jun. 16, 2009	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 1998
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value of options granted (in dollars per share)			$ 11.93		$ 10.33
Total intrinsic value of options exercised			$ 446	$ 625	$ 481
Proceeds from exercise of stock options			1,120	1,042	776
Unrecognized compensation cost related to stock options			282
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense			$ 363	$ 506	$ 601
Unrecognized compensation cost related to stock options, weighted average period for recognition			2 years
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	1,000,000					550,000
Additional shares authorized	250,000	200,000
Number of shares available for grant			313,169

Stock-Based Compensation (Valua

Stock-Based Compensation (Valuation Assumptions) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk free rate	2.12%	1.56%
Expected life	6 years	6 years
Expected volatility	39.59%	45.07%
Expected dividend yield	0.00%	0.00%

Stock-Based Compensation (Sto48

Stock-Based Compensation (Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of Shares
Outstanding, beginning of period (in shares)	350,186	414,769	432,269
Granted (in shares)	32,750	0	50,000
Exercised (in shares)	(55,666)	(62,083)	(66,000)
Canceled/Forfeited (in shares)		(2,500)	(1,500)
Outstanding, end of period (in shares)	327,270	350,186	414,769	432,269
Exercisable (in shares)	278,689
Weighted Average Grant Date Fair Value
Outstanding, beginning of period (in dollars per share)	$ 19.45	$ 19.07	$ 17.55
Granted (in dollars per share)	28.15	0	22.90
Exercised (in dollars per share)	20.12	16.79	11.76
Canceled/Forfeited, weighted average exercise price (in dollars per share)		22.90	30.41
Outstanding, end of period (in dollars per share)	20.21	$ 19.45	$ 19.07	$ 17.55
Exercisable (in dollars per share)	$ 19.12
Weighted Average Remaining Contractual Life (years)
Outstanding, weighted average remaining contractual life	4 years 2 months 41 days	4 years 2 months 29 days	5 years 28 days	4 years 8 months 81 days
Exercisable, weighted average remaining contractual life	3 years 5 months 45 days
Aggregate Intrinsic Value
Outstanding, aggregate intrinsic value	$ 2,255	$ 4,453	$ 1,814	$ 2,786
Exercised, aggregate intrinsic value	446	$ 625	$ 481
Exercisable, aggregate intrinsic value	$ 2,203

Stock-Based Compensation (Sto49

Stock-Based Compensation (Stock Options by Exercise Price Range) (Details)	12 Months Ended
	Dec. 31, 2017$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding, shares | shares	327,270
Options outstanding, weighted average remaining contractual life	4 years 2 months 43 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 20.21
Options exercisable, shares | shares	278,689
Options exercisable, weighted average exercise price (in dollars per share)	$ 19.12
Range of Exercise Prices: $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	65,852
Options outstanding, weighted average remaining contractual life	1 year 5 months 52 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 9.82
Options exercisable, shares | shares	65,852
Options exercisable, weighted average exercise price (in dollars per share)	$ 9.82
Range of Exercise Prices: $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	72,750
Options outstanding, weighted average remaining contractual life	1 year 7 months 75 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 17.53
Options exercisable, shares | shares	72,750
Options exercisable, weighted average exercise price (in dollars per share)	$ 17.53
Range of Exercise Prices: $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	56,750
Options outstanding, weighted average remaining contractual life	3 years 5 months 45 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 19.36
Options exercisable, shares | shares	56,750
Options exercisable, weighted average exercise price (in dollars per share)	$ 19.36
Range of Exercise Prices: $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	131,918
Options outstanding, weighted average remaining contractual life	7 years 3 months 33 days
Options outstanding, weighted average exercise price (in dollars per share)	$ 27.23
Options exercisable, shares | shares	83,337
Options exercisable, weighted average exercise price (in dollars per share)	$ 27.70

Stock-Based Compensation (Summa

Stock-Based Compensation (Summary of Unvested Stock Options) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Unvested, beginning of period (in shares)	50,833
Granted (in shares)	32,750	0	50,000
Vested (in shares)	(35,002)
Unvested, end of period (in shares)	48,581	50,833
Weighted Average Grant Date Fair Value
Unvested, beginning of period (in dollars per share)	$ 12.67
Granted (in dollars per share)	11.93		$ 10.33
Vested (in dollars per share)	13.73
Unvested, end of period (in dollars per share)	$ 11.41	$ 12.67

Commitments and Contingencies51

Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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	$ 301	$ 295	$ 387
Operating leases, maximum term	5 years
Operating leases, rent expense	$ 310	$ 325	$ 375

Commitments and Contingencies52

Commitments and Contingencies (Future Lease Payments) (Details) $ in Thousands	Dec. 31, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,018	$ 484
2,019	122
2,020	9
2,021	1
Total	$ 616

Quarterly Financial Data (Detai

Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Data [Abstract]
Total revenue	$ 16,660	$ 15,913	$ 16,218	$ 18,902	$ 16,703	$ 16,181	$ 17,194	$ 21,576	$ 67,693	$ 71,654	$ 95,919
Operating income	217	593	414	343	967	1,823	1,873	3,767	1,567	8,430	15,147
Net income	$ 18,702	$ 522	$ 375	$ 252	$ 1,160	$ 1,509	$ 1,259	$ 2,541	$ 19,851	$ 6,469	$ 10,147
Net income per share - Basic (in dollars per share)	$ 1.46	$ 0.04	$ 0.03	$ 0.02	$ 0.09	$ 0.12	$ 0.10	$ 0.20	$ 1.55	$ 0.51	$ 0.81
Net income per share - Diluted (in dollars per share)	$ 1.42	$ 0.04	$ 0.03	$ 0.02	$ 0.09	$ 0.12	$ 0.10	$ 0.20	$ 1.51	$ 0.50	$ 0.79