LEASES - Supplemental Balance Sheet Information (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Lease right-of-use assets	$ 30,999	$ 0
Current portion of operating lease liability	6,513	$ 0
Lease liabilities - non-current	25,967
Operating lease liability	$ 32,480
Weighted-average remaining lease term (in years)	7 years
Weighted-average discount rate	3.06%
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccruedLiabilitiesCurrent	us-gaap:AccruedLiabilitiesCurrent
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent