Revenue from Contract with Customers - Disaggregate Revenue (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Disaggregation of Revenue
Contract revenue	$ 212,040
Contract Operations
Disaggregation of Revenue
Contract revenue	161,197
Contract Operations | Transferred at point in time
Disaggregation of Revenue
Contract revenue	1,300
Contract Operations | 0 - 1000 horsepower per unit
Disaggregation of Revenue
Contract revenue	59,592
Contract Operations | 1,001 - 1,500 horsepower per unit
Disaggregation of Revenue
Contract revenue	66,230
Contract Operations | Over 1,500 horsepower per unit
Disaggregation of Revenue
Contract revenue	34,410
Contract Operations | Other
Disaggregation of Revenue
Contract revenue	965
Aftermarket Services
Disaggregation of Revenue
Contract revenue	50,843
Aftermarket Services | Services
Disaggregation of Revenue
Contract revenue	32,207
Aftermarket Services | OTC parts and components sales
Disaggregation of Revenue
Contract revenue	$ 18,636