Contract Assets and Liabilities - Components of Contract Asset and Liability Balances (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Contract assets
Costs and estimated earnings in excess of billing on uncompleted contracts	$ 44,315		$ 33,943
Retainage receivable	32,873		29,867
Total contract assets	77,188	$ 0	63,810
Change in costs in excess of billings and estimated earnings	10,372
Change in retainage receivable	3,006
Change in total contract assets	13,378
Contract liabilities
Billings in excess of costs and estimated earnings on uncompleted contracts	40,662		46,968
Provisions for losses	1,708		1,848
Total contract liabilities	42,370		$ 48,816
Change in billings in excess of costs and estimated earnings	(6,306)
Change in provisions for losses	(140)
Change in total contract liabilities	$ (6,446)	$ 0