REVENUE FROM CONTRACTS WITH CUSTOMERS - Schedule of Revenue From Contracts with Customers by Segment (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Net interest income	$ 115,922	$ 110,859	$ 118,301	$ 110,036	$ 104,934	$ 97,465	$ 101,405	$ 84,057	$ 79,760	$ 72,151	$ 83,800	$ 71,613	$ 455,118	$ 387,861	$ 307,324
Gain on trademarks													0	10,000	50,000
Gain (loss) on sale of other													12,669	2,663	(6,207)
Other income													23,167	22,115
Total noninterest income	$ 52,010	$ 65,871	$ 128,945	$ 52,761	$ 56,051	$ 67,733	$ 127,038	$ 65,777	$ 43,456	$ 53,994	$ 109,766	$ 86,591	299,587	316,599	293,807
Revenue													754,705	704,460
Refund transfer product fees
Disaggregation of Revenue [Line Items]
Noninterest income:													40,178	39,452	39,809
Refund advance fee income
Disaggregation of Revenue [Line Items]
Noninterest income:													43,473	37,433	40,557
Card and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													125,943	150,746
Rental income
Disaggregation of Revenue [Line Items]
Noninterest income:													54,157	54,190	46,558
Consumer
Disaggregation of Revenue [Line Items]
Net interest income													236,011	154,316	98,366
Gain on trademarks													0	0
Gain (loss) on sale of other													(5)	0
Other income													8,512	6,956
Total noninterest income													217,107	233,544	189,252
Revenue													453,118	387,860
Consumer | Refund transfer product fees
Disaggregation of Revenue [Line Items]
Noninterest income:													40,178	39,452
Consumer | Refund advance fee income
Disaggregation of Revenue [Line Items]
Noninterest income:													43,473	37,433
Consumer | Card and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													124,949	149,703
Consumer | Rental income
Disaggregation of Revenue [Line Items]
Noninterest income:													0	0
Commercial
Disaggregation of Revenue [Line Items]
Net interest income													194,967	195,239
Gain on trademarks													0	0
Gain (loss) on sale of other													7,702	2,005
Other income													9,636	9,682
Total noninterest income													71,748	66,051
Revenue													266,715	261,290
Commercial | Refund transfer product fees
Disaggregation of Revenue [Line Items]
Noninterest income:													0	0
Commercial | Refund advance fee income
Disaggregation of Revenue [Line Items]
Noninterest income:													0	0
Commercial | Card and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													967	1,018
Commercial | Rental income
Disaggregation of Revenue [Line Items]
Noninterest income:													53,443	53,346
Corporate Services/Other
Disaggregation of Revenue [Line Items]
Net interest income													24,140	38,306	21,749
Gain on trademarks													0	10,000
Gain (loss) on sale of other													4,972	658
Other income													5,019	5,477
Total noninterest income													10,732	17,004	$ 36,143
Revenue													34,872	55,310
Corporate Services/Other | Refund transfer product fees
Disaggregation of Revenue [Line Items]
Noninterest income:													0	0
Corporate Services/Other | Refund advance fee income
Disaggregation of Revenue [Line Items]
Noninterest income:													0	0
Corporate Services/Other | Card and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													27	25
Corporate Services/Other | Rental income
Disaggregation of Revenue [Line Items]
Noninterest income:													$ 714	$ 844