Construction Contracts - Summary of Net Position (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Contractors [Abstract]
Costs incurred on uncompleted construction contracts	$ 542,790	$ 520,368
Estimated earnings	18,673	18,070
Billings	(563,383)	(541,784)
Net position	(1,920)	(3,346)
Construction contract costs and estimated earnings in excess of billings	315	245
Billings in excess of construction contract costs and estimated earnings	$ (2,235)	$ (3,591)