SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Oct. 01, 2019	Sep. 30, 2019	Oct. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability	$ 32,480
Long-term right of use assets	$ 30,999		$ 0
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease liability		$ 30,881
Long-term right of use assets		30,115
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect of the adoption of the stranded tax effect accounting standard		0		$ (933)
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effect of the adoption of the stranded tax effect accounting standard		$ 488		$ (933)