Fair Value of Financial Instruments - Fair Value Disclosure (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Assets:
Interest rate swap (See Note 15)	$ 12,335	$ 0
Fair value, measurements, recurring
Assets:
Cash and cash equivalents	185,979	257,354
Other long-term investments	1,439	1,214
Interest rate swap (See Note 15)	12,335	27
Total assets	199,753	258,595
Liabilities:
Derivative financial instruments	3,383	38,157
Total liabilities	3,383	38,157
Fair value, measurements, recurring | Level 1
Assets:
Cash and cash equivalents	185,979	257,354
Other long-term investments	1,439	1,214
Interest rate swap (See Note 15)	0	0
Total assets	187,418	258,568
Liabilities:
Derivative financial instruments	0	0
Total liabilities	0	0
Fair value, measurements, recurring | Level 2
Assets:
Cash and cash equivalents	0	0
Other long-term investments	0	0
Interest rate swap (See Note 15)	12,335	27
Total assets	12,335	27
Liabilities:
Derivative financial instruments	3,383	38,157
Total liabilities	3,383	38,157
Fair value, measurements, recurring | Level 3
Assets:
Cash and cash equivalents	0	0
Other long-term investments	0	0
Interest rate swap (See Note 15)	0	0
Total assets	0	0
Liabilities:
Derivative financial instruments	0	0
Total liabilities	$ 0	$ 0