Captive Insurance Collateral - Schedule of Maturities of Investments (Detail) - USD ($) $ in Thousands		Jun. 30, 2019	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Due within one year		$ 8,027
Due after one year through five years		35,554
Due after five years through ten years		14,260
Total	[1]	$ 57,841	$ 45,419

[1] See Note 2 – Summary of Significant Accounting Policies – Captive Insurance Collateral.