Revenue from Contract with Customers - Disaggregate Revenue (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Disaggregation of Revenue
Contract revenue	$ 220,316	$ 238,390	$ 470,013	$ 474,549
Number of reportable segments | segment			2
Contract Operations
Disaggregation of Revenue
Contract revenue	187,949	186,258	$ 394,923	368,765
Contract Operations | Transferred at Point in Time
Disaggregation of Revenue
Contract revenue	1,500	2,200	3,100	4,400
Contract Operations | 0 - 1,000 horsepower per unit
Disaggregation of Revenue
Contract revenue	57,728	63,683	124,468	127,422
Contract Operations | 1,001 - 1,500 horsepower per unit
Disaggregation of Revenue
Contract revenue	78,026	75,598	162,878	149,938
Contract Operations | Over 1,500 horsepower per unit
Disaggregation of Revenue
Contract revenue	51,618	45,969	106,209	89,394
Contract Operations | Other
Disaggregation of Revenue
Contract revenue	577	1,008	1,368	2,011
Aftermarket Services
Disaggregation of Revenue
Contract revenue	32,367	52,132	75,090	105,784
Aftermarket Services | Services
Disaggregation of Revenue
Contract revenue	19,081	33,281	44,531	66,802
Aftermarket Services | OTC parts and components sales
Disaggregation of Revenue
Contract revenue	$ 13,286	$ 18,851	$ 30,559	$ 38,982