Contract Assets and Liabilities - Components of Contract Asset and Liability Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Contract assets
Costs in excess of billings and estimated earnings	$ 38,407		$ 44,315
Retainage receivable	31,263		32,873
Total contract assets	69,670	$ 65,884	77,188
Change in costs in excess of billings and estimated earnings	(5,908)
Change in retainage receivable	(1,610)
Change in total contract assets	(7,518)	2,074
Contract liabilities
Billings in excess of costs and estimated earnings	47,451		40,662
Provisions for losses	957		1,708
Total contract liabilities	48,408		$ 42,370
Change in billings in excess of costs and estimated earnings	6,789
Change in provisions for losses	(751)
Change in total contract liabilities	$ 6,038	$ (6,521)