Captive Insurance Collateral - Schedule of Maturities of Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Due within one year	$ 9,946
Due after one year through five years	41,173
Due after five years through ten years	11,584
Total	$ 62,703	$ 58,490

Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following latest fiscal year. Excludes interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

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Balance Type:	debit
Period Type:	instant