INCOME TAXES - Changes in the Gross Unrecognized Tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 11,544	$ 1,434	$ 2,270
Additions for tax positions relating to the current fiscal year	4,691	271	263
Additions for tax positions relating to prior fiscal years	140	9,839	116
Lapse of statute of limitations			(1,215)
Reduction for tax positions relating to prior fiscal years	(1,337)
Ending balance	15,038	11,544	$ 1,434
Income tax interest and penalties accrued	$ 233	$ 281