Revenue from Contracts with Customers Revenue by Contractor Type (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenue by Contractor Type [Line Items]
Revenue	$ 648,578	$ 632,492	$ 1,281,802	$ 1,243,404
Prime contractor
Revenue by Contractor Type [Line Items]
Revenue	602,306	577,377	1,191,380	1,132,545
Subcontractor
Revenue by Contractor Type [Line Items]
Revenue	$ 46,272	$ 55,115	$ 90,422	$ 110,859