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FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Narrative (Details) - USD ($) $ in Thousands, shares in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (loss) resulting from the change in the fair value of investments		$ (8,700)
Investment shares sold (in shares)	1.6
Proceeds from sale of marketable securities	$ 12,000	0	$ 11,999	$ 0
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets held in a non-qualified supplemental savings plan	$ 15,700	$ 19,800	$ 15,700

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Marketable Securities, Shares Sold

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Carrying amount as of the balance sheet date of assets held under deferred compensation agreements.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=120269885&loc=SL75117546-209714

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The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity or available-for-sale) during the period.

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