Reportable Segments - Revenue and Gross Margin by Reportable Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Revenue and other financial information by reportable segment
Revenue from external customers	$ 189,885	$ 213,295
Gross margin	92,056	114,754
Contract Operations
Revenue and other financial information by reportable segment
Revenue from external customers	149,984	176,239
Gross margin	85,887	108,060
Aftermarket Services
Revenue and other financial information by reportable segment
Revenue from external customers	39,901	37,056
Gross margin	$ 6,169	$ 6,694