Revenue From Contracts with Customers - Disaggregate of Revenue (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Disaggregation of Revenue
Revenue	$ 245,987	$ 244,949	$ 238,390	$ 236,159	$ 233,159	$ 232,372	$ 226,870	$ 212,040	$ 965,485	$ 904,441	$ 794,655
Number of reportable segments | segment									2
Contract Operations | Transferred at Point in Time
Disaggregation of Revenue
Revenue									$ 7,900	6,600
Contract Operations | Contract operations
Disaggregation of Revenue
Revenue									771,539	672,536	$ 610,921
Contract Operations | 0 - 1,000 horsepower per unit
Disaggregation of Revenue
Revenue									259,985	241,810
Contract Operations | 1,001 - 1,500 horsepower per unit
Disaggregation of Revenue
Revenue									316,082	276,775
Contract Operations | Over 1,500 horsepower per unit
Disaggregation of Revenue
Revenue									191,510	149,783
Contract Operations | Other
Disaggregation of Revenue
Revenue									3,962	4,168
Aftermarket Services | Aftermarket Services
Disaggregation of Revenue
Revenue									193,946	231,905
Aftermarket Services | Services
Disaggregation of Revenue
Revenue									122,076	142,476
Aftermarket Services | Services | Adjustments
Disaggregation of Revenue
Revenue									(900)
Aftermarket Services | OTC parts and components sales
Disaggregation of Revenue
Revenue									$ 71,870	$ 89,429