STOCKHOLDERS’ EQUITY - Narrative (Details)		12 Months Ended
	Nov. 06, 2018 $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares	Sep. 30, 2022 USD ($) $ / shares shares	Sep. 30, 2021 USD ($) shares	Oct. 02, 2023 shares	Oct. 22, 2021 shares	Jun. 15, 2021 USD ($)	Sep. 30, 2020 shares	Jan. 31, 2020 shares	Feb. 28, 2019	Oct. 23, 2018 $ / right $ / shares shares	Mar. 07, 2018 shares	Mar. 10, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (in shares)		0	0	0
Unrecognized compensation expense related to options outstanding | $		$ 20,300,000
Weighted average period for unrecognized compensation expense expected to be recognized		2 years 3 months 18 days
Options to purchase common stock outstanding (in shares)		651,269	781,092	816,717				1,162,505
Recognized compensation expense | $		$ 10,463,000	$ 13,346,000	$ 11,532,000
Amount authorized under share repurchase program | $							$ 15,000,000
Amount of shares repurchased | $			$ 14,800,000
Number of shares repurchased (in shares)			886,204
Average price of shares repurchased (in dollars per share) | $ / shares			$ 16.73
Preferred stock, par value per share (in dollars per share) | $ / shares		$ 0.001	$ 0.001
Percentage of common stock outstanding for acquiring person under right agreement										4.90%
Series B Junior Preferred Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of preferred share purchase right for each share of common stock (in shares)											1
Preferred stock, share conversion ratio											0.001
Preferred stock, par value per share (in dollars per share) | $ / shares											$ 0.001
Preferred stock, purchase price per right (in dollars per right) | $ / right											35.00
Preferred stock, redemption price per right (in dollars per share) | $ / shares											$ 0.0001
Preferred stock, number of rights expired, redeemed or exchanged (in shares)						0
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for unrecognized compensation expense expected to be recognized		2 years 6 months
Awards outstanding (in shares)		2,188,296	2,441,677	2,411,267				2,661,943
Recognized compensation expense | $		$ 7,100,000	$ 9,400,000	$ 8,100,000
Unrecognized compensation expense | $		$ 16,700,000
Performance RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for unrecognized compensation expense expected to be recognized		1 year 8 months 12 days
Awards outstanding (in shares)		730,393	919,456	528,724				353,556
Recognized compensation expense | $		$ 2,700,000	$ 3,000,000	$ 1,300,000
Unrecognized compensation expense | $		$ 3,400,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for unrecognized compensation expense expected to be recognized		1 month 6 days
Recognized compensation expense | $		$ 400,000	500,000	700,000
Unrecognized compensation expense related to options outstanding | $		9,000
Performance Options | Chief Executive Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of common stock reserved for future grants (in shares)	800,000
Recognized compensation expense | $		$ 0	100,000	800,000
Exercise price per share (in dollars per share) | $ / shares	$ 9.50
2020 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)									4,500,000
Number of common stock reserved for future grants (in shares)		1,425,042
2020 Plan | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)					5,108,000
2020 Plan | RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards outstanding (in shares)		1,834,474
2020 Plan | Performance RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards outstanding (in shares)		730,393
Prior Plans
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)									107,903
Options to purchase common stock outstanding (in shares)		434,090
Prior Plans | RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards outstanding (in shares)		94,309
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)												1,000,000
Number of common stock reserved for future grants (in shares)		270,876
Issuance of common stock under employee stock purchase plan (in shares)		729,124
Discount rate from market price offering date		15.00%
Recognized compensation expense | $		$ 300,000	$ 400,000	$ 600,000
Director Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance (in shares)													1,500,000
Number of common stock reserved for future grants (in shares)		0
Director Plan | RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options to purchase common stock outstanding (in shares)		259,513