FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Supplemental Fair Value Information about Long-Term Fixed-Rate Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Sep. 30, 2021	Mar. 31, 2021
Supplemental fair value information about long-term fixed-rate debt
Current portion of long-term debt, net	$ 0	$ 483,486
Noncurrent portion of long term debt carrying value	541,969	$ 541,997
Carrying value
Supplemental fair value information about long-term fixed-rate debt
Current portion of long-term debt, net	0		$ 483,500
Noncurrent portion of long term debt carrying value	542,000		542,000
Fair value | Level 2
Supplemental fair value information about long-term fixed-rate debt
Current portion of long term debt fair value	0		541,600
Noncurrent portion of long term debt fair value	$ 506,900		$ 554,300