Contract Assets and Liabilities - Summary of contract assets and liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Contractors [Line Items]
Contract assets, net	$ 219,445		$ 185,803
Contract liabilities	(149,847)		(158,396)
Net contract assets (liabilities)	69,598		$ 27,407
Contract assets, net, Change	33,642	$ 4,754
Change
Contractors [Line Items]
Contract assets, net, Change	33,642
Contract liabilities, Change	8,549
Net contract assets (liabilities), Change	$ 42,191