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Captive Insurance Collateral - Schedule of Captive Insurance Collateral to be Level 1 Available-for-sale Investments (Detail) - USD ($) $ in Thousands | Jun. 30, 2021 | Sep. 30, 2020
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Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | $ 68,763 | $ 67,842
Gross Unrealized Gain | 1,187 | 1,971
Gross Unrealized (Loss) | (155) | (26)
Fair Value | 69,795 | 69,787
Cash and Receivables |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | 443 | 1,152
Fair Value | 443 | 1,152
U.S. Government Sponsored Agencies |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | 48,841 | 42,032
Gross Unrealized Gain | 125 | 229
Gross Unrealized (Loss) | (129) | (26)
Fair Value | 48,837 | 42,235
Corporate Debt Securities |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | 17,993 | 21,666
Gross Unrealized Gain | 1,017 | 1,660
Gross Unrealized (Loss) | (26) |
Fair Value | 18,984 | 23,326
Foreign Bonds and Notes |  |
Schedule Of Available For Sale Securities [Line Items] |  |
Amortized Cost | 1,486 | 2,992
Gross Unrealized Gain | 45 | 82
Gross Unrealized (Loss) | 0 | 0
Fair Value | $ 1,531 | $ 3,074

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