Costs and Estimated Earnings on Uncompleted Contracts - Costs and Estimated Earnings on Uncompleted Contracts (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Costs In Excess Of Billings On Uncompleted Contracts Or Programs [Abstract]
Costs incurred on uncompleted contracts	$ 164,400	$ 169,665
Estimated earnings	60,561	61,556
Total costs and estimated earnings on uncompleted contracts, gross	224,961	231,221
Less billings to date	(223,575)	(217,743)
Total costs and estimated earnings on uncompleted contracts, net	1,386	13,478
Included in the accompanying condensed consolidated balance sheets under the following captions:
Costs and estimated earnings in excess of billings on uncompleted contracts	29,991	33,947
Billings in excess of costs and estimated earnings on uncompleted contracts	(28,605)	(20,469)
Total costs and estimated earnings on uncompleted contracts, net	$ 1,386	$ 13,478