Contract Assets and Liabilities - Components of Contract Liabilities Balance (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Revenue From Contract With Customer [Abstract]
Billings in excess of costs and estimated earnings, net of retention	$ 88,595	$ 103,250	$ 70,398
Provisions for losses	2,157	2,199	632
Total contract liabilities	$ 90,752	$ 105,449	$ 71,030