SHARE-BASED COMPENSATION PLANS - Schedule of Total Gross Share-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Gross share-based compensation expense	$ 4,406	$ 4,267	$ 6,392
Restricted stock, restricted stock units, and replacement awards
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Gross share-based compensation expense	8,259	11,400	9,186
Performance share units
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Gross share-based compensation expense	1,957	1,279	2,056
ESPP
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Gross share-based compensation expense	$ 1,774	$ 1,281	$ 885