Captive Insurance Collateral - Schedule of Maturities of Investments (Detail) - USD ($) $ in Thousands		Mar. 31, 2019	Sep. 30, 2018
Investments Debt And Equity Securities [Abstract]
Due within one year		$ 5,333
Due after one year through five years		33,865
Due after five years through ten years		14,950
Total	[1]	$ 54,148	$ 45,419

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