Contract Assets and Liabilities - Cost and Estimated Earnings Compared to Billings on Uncompleted Contracts (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Contractors [Abstract]
Costs on uncompleted contracts	$ 900,880	$ 743,322
Estimated earnings to date on uncompleted contracts	123,256	95,155
Costs and estimated earnings to date on uncompleted contracts	1,024,136	838,477
Billings to date on uncompleted contracts	(1,043,221)	(867,881)
Net billings in excess of costs and estimated earnings on uncompleted contracts	$ 19,085	$ 29,404