Contracts in Progress and Advance Billings on Contracts - Schedule of Contract Assets and Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Contractors [Abstract]
Costs incurred less costs of revenues recognized	$ (3,228)	$ 98,127
Revenues recognized less billings to customers	509,648	523,284
Contracts in Progress, assets	506,420	621,411
Billings to customers less revenues recognized	28,279	45,661
Costs incurred less costs of revenues recognized	11,928	(13,409)
Advance billings on contracts	$ 40,207	$ 32,252