Costs and Estimated Earnings on Uncompleted Contracts - Activity (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Revenue Recognition and Deferred Revenue [Abstract]
Costs incurred on uncompleted contracts	$ 369,753	$ 314,700
Estimated earnings	84,624	96,176
Total costs and estimated earnings	454,377	410,876
Less billings to date	(364,162)	(325,518)
Costs and estimated earnings in excess of billings	$ 90,215	$ 85,358