Segments - Revenue and Gross Margin by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue and other financial information by reportable segment
Revenues	$ 220,316	$ 238,390	$ 470,013	$ 474,549
Gross margin	128,240	125,654	264,295	243,176
Contract Operations
Revenue and other financial information by reportable segment
Revenues	187,949	186,258	394,923	368,765
Gross margin	124,559	115,737	252,882	223,509
Aftermarket Services
Revenue and other financial information by reportable segment
Revenues	32,367	52,132	75,090	105,784
Gross margin	$ 3,681	$ 9,917	$ 11,413	$ 19,667