PARENT COMPANY FINANCIAL STATEMENTS - Cash Flow Statement (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
Cash flows from operating activities:
Net income attributable to parent	$ 23,420	$ 22,391	$ 49,251	$ 61,324	$ 15,903	$ 38,701	$ 59,066	$ 28,037	$ 13,158	$ 18,190	$ 52,304	$ 21,068	$ 156,386	$ 141,708	$ 104,720
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation, amortization and accretion, net													61,601	59,047	60,745
Net change in accrued interest receivable													(1,725)	374	2,050
Net change in other assets													(32,936)	825	1,524
Net change in accrued expenses and other liabilities													(10,640)	43,920	1,152
Stock compensation													10,004	6,852	10,221
Net cash provided by operating activities													268,809	581,645	467,220
Cash flows from investing activities:
Net cash (used in) investing activities													(310,872)	(1,118,402)	(206,316)
Cash flows from financing activities:
Redemption of long-term borrowings													(75,000)	0	0
Proceeds from long-term borrowings													20,000	0	0
Dividends paid on common stock													(5,921)	(6,400)	(7,100)
Issuance of common stock due to exercise of stock options													0	0	266
Issuance of common stock due to restricted stock													1	0	2
Repurchases of common stock													(168,235)	(99,878)	(118,738)
Net cash provided by financing activities													117,818	422,933	40,019
Net change in cash and cash equivalents													74,019	(113,348)	300,822
Cash and cash equivalents at beginning of fiscal year				314,019				427,367				126,545	314,019	427,367	126,545
Cash and cash equivalents at end of fiscal period	388,038				314,019				427,367				388,038	314,019	427,367
Meta Financial
Cash flows from operating activities:
Net income attributable to parent													156,386	141,708	104,720
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation, amortization and accretion, net													1,020	173	163
Equity in undistributed net income of subsidiaries													(159,652)	(147,895)	(107,476)
Net change in accrued interest receivable													(15)	0	0
Net change in other assets													(636)	3,030	(3,149)
Net change in accrued expenses and other liabilities													3,163	(2,698)	(2,660)
Cash dividend received													229,200	104,000	118,000
Stock compensation													10,004	6,852	10,221
Net cash provided by operating activities													239,470	105,170	119,819
Cash flows from investing activities:
Alternative investments													(3,380)	(3,415)	(797)
Net cash (used in) investing activities													(3,380)	(3,415)	(797)
Cash flows from financing activities:
Redemption of long-term borrowings													(75,000)	0	0
Proceeds from long-term borrowings													20,000	0	0
Dividends paid on common stock													(5,921)	(6,400)	(7,100)
Issuance of common stock due to exercise of stock options													0	0	266
Issuance of common stock due to restricted stock													1	0	2
Issuance of common stock due to ESOP													2,886	3,036	3,220
Repurchases of common stock													(168,235)	(99,878)	(118,738)
Net cash provided by financing activities													(226,269)	(103,242)	(122,350)
Net change in cash and cash equivalents													9,821	(1,487)	(3,328)
Cash and cash equivalents at beginning of fiscal year				$ 3,296				$ 4,783				$ 8,111	3,296	4,783	8,111
Cash and cash equivalents at end of fiscal period	$ 13,117				$ 3,296				$ 4,783				$ 13,117	$ 3,296	$ 4,783