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Revenue Recognition - Schedule of Net Under (Over) Billings (Detail) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Contractors [Abstract]    
Costs and estimated earnings in excess of billings on uncompleted contracts (contract assets) $ 19,565 $ 15,092
Billings in excess of costs and estimated earnings on uncompleted contracts (contract liabilities) (4,971) (4,426)
Net under (over) billings $ 14,594 $ 10,666