Costs and Estimated Earnings on Uncompleted Contracts - Costs and Estimated Earnings on Uncompleted Contracts (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Costs In Excess Of Billings On Uncompleted Contracts Or Programs [Abstract]
Costs incurred on uncompleted contracts	$ 193,393	$ 174,168
Estimated earnings	76,693	67,427
Total costs and estimated earnings on uncompleted contracts, gross	270,086	241,595
Less billings to date	(261,981)	(232,045)
Total costs and estimated earnings on uncompleted contracts, net	8,105		$ 9,550
Included in the accompanying condensed consolidated balance sheets under the following captions:
Costs and estimated earnings in excess of billings on uncompleted contracts	31,701	29,694	29,694
Billings in excess of costs and estimated earnings on uncompleted contracts	(23,596)	$ (20,144)	(20,144)
Total costs and estimated earnings on uncompleted contracts, net	$ 8,105		$ 9,550