Revenue from Contracts with Customers Revenue by Contractor Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue by Contractor Type [Line Items]
Revenue	$ 633,224	$ 610,912
Prime contractor
Revenue by Contractor Type [Line Items]
Revenue	589,074	555,168
Subcontractor
Revenue by Contractor Type [Line Items]
Revenue	$ 44,150	$ 55,744