SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RELATED RISKS AND UNCERTAINTIES - Restricted Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022	Sep. 30, 2021
Restricted Cash and Investments
Cash and cash equivalents	$ 159,672	$ 232,131	$ 202,206	$ 917,534
Restricted cash and cash equivalents	53,200	36,900	27,200	19,200
Total cash, cash equivalents, and restricted cash	212,903	269,009	229,376	936,716
Restricted cash
Restricted Cash and Investments
Restricted cash and cash equivalents	53,231	36,246	26,438	18,350
Other assets, net
Restricted Cash and Investments
Restricted cash and cash equivalents	$ 0	$ 632	$ 732	$ 832

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(2))
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(1))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1)(a))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant