Segments - Revenue and Gross Margin by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue and other financial information by reportable segment
Revenues	$ 205,631	$ 244,949	$ 675,644	$ 719,498
Gross margin	119,478	131,383	383,773	374,559
Contract Operations
Revenue and other financial information by reportable segment
Revenues	175,223	198,337	570,146	567,102
Gross margin	114,779	122,396	367,661	345,905
Aftermarket Services
Revenue and other financial information by reportable segment
Revenues	30,408	46,612	105,498	152,396
Gross margin	$ 4,699	$ 8,987	$ 16,112	$ 28,654