Revenue from Contract with Customers - Disaggregate Revenue (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) segment	Sep. 30, 2017 USD ($)
Disaggregation of Revenue
Number of reportable segments | segment			2
Contract revenue	$ 232,372	$ 197,853	$ 671,282	$ 585,720
Contract Operations | Transferred at point in time
Disaggregation of Revenue
Contract revenue	1,600		4,300
Contract Operations | Contract operations
Disaggregation of Revenue
Contract revenue	169,509	153,524	496,156	454,622
Contract Operations | 0 - 1000 horsepower per unit
Disaggregation of Revenue
Contract revenue	60,725		179,917
Contract Operations | 1,001 - 1,500 horsepower per unit
Disaggregation of Revenue
Contract revenue	69,663		204,841
Contract Operations | Over 1,500 horsepower per unit
Disaggregation of Revenue
Contract revenue	38,053		108,367
Contract Operations | Other
Disaggregation of Revenue
Contract revenue	1,068		3,031
Aftermarket Services | Aftermarket services
Disaggregation of Revenue
Contract revenue	62,863	$ 44,329	175,126	$ 131,098
Aftermarket Services | Services
Disaggregation of Revenue
Contract revenue	38,863		107,776
Aftermarket Services | OTC parts and components sales
Disaggregation of Revenue
Contract revenue	$ 24,000		$ 67,350