Revenue from Contracts with Customers Revenue by Contractor Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue by Contractor Type [Line Items]
Revenue	$ 636,196	$ 579,179	$ 1,879,600	$ 1,618,146
Prime contractor
Revenue by Contractor Type [Line Items]
Revenue	579,858	524,370	1,712,403	1,448,875
Subcontractor
Revenue by Contractor Type [Line Items]
Revenue	$ 56,338	$ 54,809	$ 167,197	$ 169,271