RESTRUCTURING CHARGES - Summary of Accrued Liability for the Restructuring and Related Charges (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2021
Restructuring Reserve [Roll Forward]
Accrued liability beginning balance	$ 3,839	$ 2,965	$ 2,965
Restructuring charges	7,562	10,800
Cash payment	(8,113)	(4,132)
Non-cash charges	(2,497)	(5,794)
Accrued liability ending balance	791	3,839	791
Personnel related costs
Restructuring Reserve [Roll Forward]
Accrued liability beginning balance	3,585	2,701	2,701
Restructuring charges	782	2,482
Cash payment	(3,840)	(1,598)
Non-cash charges	0	0
Accrued liability ending balance	527	3,585	527
Facilities, exit costs and other
Restructuring Reserve [Roll Forward]
Accrued liability beginning balance	254	264	264
Restructuring charges	4,283	2,524
Cash payment	(4,273)	(2,534)
Non-cash charges	0	0
Accrued liability ending balance	264	254	264
Facility and Other Costs
Restructuring Reserve [Roll Forward]
Accrued liability beginning balance	0	0	0
Restructuring charges	2,497	5,794
Cash payment	0	0
Non-cash charges	(2,497)	(5,794)
Accrued liability ending balance	$ 0	$ 0	$ 0