Basis of Presentation and Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies These notes apply to the unaudited condensed consolidated financial statements of Natural Gas Services Group, Inc. a Colorado corporation (the "Company", “NGSG”, "Natural Gas Services Group", "we" or "our"). The accompanying unaudited condensed consolidated financial statements include all adjustments, consisting of only normal recurring adjustments, which are necessary to make our financial position at September 30, 2017 and the results of our operations for the three and nine months ended September 30, 2017 and 2016 not misleading. As permitted by the rules and regulations of the Securities and Exchange Commission (SEC), the accompanying condensed consolidated financial statements do not include all disclosures normally required by generally accepted accounting principles in the United States of America (GAAP). These financial statements should be read in conjunction with the financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2016 on file with the SEC. In our opinion, the condensed consolidated financial statements are a fair presentation of the financial position, results of operations and cash flows for the periods presented. The results of operations for the three and nine months ended September 30, 2017 are not necessarily indicative of the results of operations to be expected for the full fiscal year ending December 31, 2017. 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. From time to time, we have customers that request units and flares to be built under a bill and hold arrangement. In order to recognize revenue under a bill and hold arrangement the following criteria must be met: risk of ownership was passed to the customer, customer made a fixed commitment to purchase the goods, the customer requested the bill and hold, there was a fixed schedule for delivery, we no longer had any specific performance obligations, the purchase was segregated at our facility and the equipment was complete and ready to ship. For the nine months ended September 30, 2017, we recognized revenue of $5.7 million under these bill and hold arrangements. Exchange and rebuilt compressor revenue is recognized when 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. Fair Value of Financial Instruments Our financial instruments consist principally of cash and cash equivalents, accounts receivable, accounts payable, deferred compensation plan (cash portion) and our line of credit. Pursuant to ASC 820 (Accounting Standards Codification), the fair value of our cash equivalents is determined based on “Level 1” inputs, which consist of quoted prices in active markets for identical assets. We believe that the recorded values of all of our other financial instruments approximate their fair values because of their nature and relatively short maturity dates or durations. 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 condensed 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 expect to adopt this guidance on January 1, 2018. The guidance offers 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 preliminarily selected the modified retrospective transition method. We are currently determining the impacts of the new standard on our consolidated financial statements. Our approach includes 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. Our sales and service and maintenance contracts are more short-term in nature or can usually be completed within the same quarter they are started; but, at this stage in our assessment we are still finalizing our evaluation of the extent to which we will have changes, upon adoption. For the impact related to our rental revenues, we are in the final stages of our review and have not concluded as to what impact, if any, there may be to our rental revenues. We also tentatively anticipate a change in our disclosures under the new standard. We expect to complete our review by mid-November 2017.

Basis of Presentation and Summary of Significant Accounting Policies

These notes apply to the unaudited condensed consolidated financial statements of Natural Gas Services Group, Inc. a Colorado corporation (the "Company", “NGSG”, "Natural Gas Services Group", "we" or "our").

The accompanying unaudited condensed consolidated financial statements include all adjustments, consisting of only normal recurring adjustments, which are necessary to make our financial position at September 30, 2017 and the results of our operations for the three and nine months ended September 30, 2017 and 2016 not misleading. As permitted by the rules and regulations of the Securities and Exchange Commission (SEC), the accompanying condensed consolidated financial statements do not include all disclosures normally required by generally accepted accounting principles in the United States of America (GAAP). These financial statements should be read in conjunction with the financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2016 on file with the SEC. In our opinion, the condensed consolidated financial statements are a fair presentation of the financial position, results of operations and cash flows for the periods presented.

The results of operations for the three and nine months ended September 30, 2017 are not necessarily indicative of the results of operations to be expected for the full fiscal year ending December 31, 2017.

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. From time to time, we have customers that request units and flares to be built under a bill and hold arrangement. In order to recognize revenue under a bill and hold arrangement the following criteria must be met: risk of ownership was passed to the customer, customer made a fixed commitment to purchase the goods, the customer requested the bill and hold, there was a fixed schedule for delivery, we no longer had any specific performance obligations, the purchase was segregated at our facility and the equipment was complete and ready to ship. For the nine months ended September 30, 2017, we recognized revenue of $5.7 million under these bill and hold arrangements. Exchange and rebuilt compressor revenue is recognized when 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.

Fair Value of Financial Instruments

Our financial instruments consist principally of cash and cash equivalents, accounts receivable, accounts payable, deferred compensation plan (cash portion) and our line of credit. Pursuant to ASC 820 (Accounting Standards Codification), the fair value of our cash equivalents is determined based on “Level 1” inputs, which consist of quoted prices in active markets for identical assets. We believe that the recorded values of all of our other financial instruments approximate their fair values because of their nature and relatively short maturity dates or durations.

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 condensed 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 expect to adopt this guidance on January 1, 2018. The guidance offers 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 preliminarily selected the modified retrospective transition method. We are currently determining the impacts of the new standard on our consolidated financial statements. Our approach includes 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. Our sales and service and maintenance contracts are more short-term in nature or can usually be completed within the same quarter they are started; but, at this stage in our assessment we are still finalizing our evaluation of the extent to which we will have changes, upon adoption. For the impact related to our rental revenues, we are in the final stages of our review and have not concluded as to what impact, if any, there may be to our rental revenues. We also tentatively anticipate a change in our disclosures under the new standard. We expect to complete our review by mid-November 2017.