Contract Assets and Liabilities - Summary of contract assets and liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Contractors [Line Items]
Contract assets, net	$ 196,873		$ 185,803
Contract liabilities	(136,987)		(158,396)
Net contract assets (liabilities)	59,886		$ 27,407
Contract assets, net, Change	10,855	$ 7,658
Change
Contractors [Line Items]
Contract assets, net, Change	11,070
Contract liabilities, Change	21,409
Net contract assets (liabilities), Change	$ 32,479