Contract Assets and Liabilities - Summary of assets and liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Contractors [Line Items]
Contract assets, net	$ 224,275		$ 217,109
Contract liabilities	(128,702)		(105,486)
Net contract assets (liabilities)	95,573		$ 111,623
Changes in contract assets, net	7,658	$ 14,218
Net Period Change [Member]
Contractors [Line Items]
Changes in contract assets, net	7,166
Changes in contract liabilities	(23,216)
Changes in net contract assets (liabilities)	$ (16,050)