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, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Net interest income (expense)	$ 79,760	$ 72,151	$ 83,800	$ 71,613	$ 70,667	$ 68,475	$ 73,850	$ 65,999	$ 64,513	$ 62,137	$ 67,737	$ 64,651	$ 307,324	$ 278,991	$ 259,038
Gain (loss) on sale of securities													(1,287)	6	51
Gain on sale of trademarks													50,000	0	0
Gain (loss) on sale of other													(4,920)	11,515	4,425
Other income													17,357	26,240	14,641
Noninterest income	$ 43,456	$ 53,994	$ 109,766	$ 86,591	$ 49,542	$ 62,453	$ 113,453	$ 45,455	$ 40,750	$ 41,048	$ 120,513	$ 37,483	293,807	270,904	239,794
Revenue													601,131	549,895
Refund transfer product fees
Disaggregation of Revenue [Line Items]
Noninterest income:													39,809	37,967
Refund advance fee income
Disaggregation of Revenue [Line Items]
Noninterest income:													40,557	47,639	31,826
Payment card and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													104,684	107,182
Other bank and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													1,049	939	1,310
Rental income
Disaggregation of Revenue [Line Items]
Noninterest income:													46,558	39,416	44,826
Consumer
Disaggregation of Revenue [Line Items]
Net interest income (expense)													98,366	91,489	92,362
Gain (loss) on sale of securities													0	0
Gain on sale of trademarks													0	0
Gain (loss) on sale of other													0	0
Other income													4,202	2,902
Noninterest income													189,252	195,708	158,284
Revenue													287,618	287,197
Consumer | Refund transfer product fees
Disaggregation of Revenue [Line Items]
Noninterest income:													39,809	37,967
Consumer | Refund advance fee income
Disaggregation of Revenue [Line Items]
Noninterest income:													40,557	47,639
Consumer | Payment card and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													104,684	107,182
Consumer | Other bank and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													0	0
Consumer | Rental income
Disaggregation of Revenue [Line Items]
Noninterest income:													0	18
Commercial
Disaggregation of Revenue [Line Items]
Net interest income (expense)													187,209	173,969	151,649
Gain (loss) on sale of securities													0	0
Gain on sale of trademarks													0	0
Gain (loss) on sale of other													8,782	12,622
Other income													12,587	8,876
Noninterest income													68,412	61,813	60,151
Revenue													255,621	235,782
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 | Payment card and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													0	0
Commercial | Other bank and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													1,020	917
Commercial | Rental income
Disaggregation of Revenue [Line Items]
Noninterest income:													46,023	39,398
Corporate Services/Other
Disaggregation of Revenue [Line Items]
Net interest income (expense)													21,749	13,533	15,027
Gain (loss) on sale of securities													(1,287)	6
Gain on sale of trademarks													50,000	0
Gain (loss) on sale of other													(13,702)	(1,107)
Other income													568	14,462
Noninterest income													36,143	13,383	$ 21,359
Revenue													57,892	26,916
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 | Payment card and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													0	0
Corporate Services/Other | Other bank and deposit fees
Disaggregation of Revenue [Line Items]
Noninterest income:													29	22
Corporate Services/Other | Rental income
Disaggregation of Revenue [Line Items]
Noninterest income:													$ 535	$ 0