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Revenue Recognition - Schedule of Net Under (Over) Billings (Detail) - USD ($)
$ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2019
Dec. 31, 2018
Contractors [Abstract]    
Costs and estimated earnings in excess of billings on uncompleted contracts (contract assets) $ 22,278 $ 15,092
Billings in excess of costs and estimated earnings on uncompleted contracts (contract liabilities) (5,524) (4,426)
Net under billings $ 16,754 $ 10,666