Captive Insurance Collateral - Schedule of Captive Insurance Collateral to be Level 1 Available-for-sale Investments (Detail) - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 68,574	$ 67,842
Gross Unrealized Gain	1,195	1,971
Gross Unrealized (Loss)	(116)	(26)
Fair Value	69,653	69,787
Cash and Receivables
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	913	1,152
Fair Value	913	1,152
U.S. Government Sponsored Agencies
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	47,154	42,032
Gross Unrealized Gain	134	229
Gross Unrealized (Loss)	(60)	(26)
Fair Value	47,228	42,235
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	19,020	21,666
Gross Unrealized Gain	1,009	1,660
Gross Unrealized (Loss)	(56)
Fair Value	19,973	23,326
Foreign Bonds and Notes
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	1,487	2,992
Gross Unrealized Gain	52	82
Gross Unrealized (Loss)	0	0
Fair Value	$ 1,539	$ 3,074

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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