PARENT COMPANY FINANCIAL STATEMENTS - Cash Flow Statement (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
Cash flows from operating activities:
Net income attributable to parent	$ 33,597	$ 41,835	$ 65,268	$ 27,657	$ 35,906	$ 45,096	$ 54,771	$ 27,842	$ 23,420	$ 22,391	$ 49,251	$ 61,324	$ 168,357	$ 163,615	$ 156,386
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation, amortization and accretion, net													57,765	64,955	61,601
Net change in accrued interest receivable													(8,103)	(5,303)	(1,725)
Net change in other assets													(11,747)	17,134	(32,936)
Net change in accrued expenses and other liabilities													176,083	48,658	(10,640)
Stock compensation													10,286	11,070	10,004
Net cash provided by operating activities													453,537	303,111	268,809
Cash flows from investing activities:
Net cash (used in) investing activities													(227,661)	(920,758)	(310,872)
Cash flows from financing activities:
Redemption of long-term borrowings													0	0	(75,000)
Payment of debt issuance costs													0	(511)	0
Proceeds from long-term borrowings													0	0	20,000
Dividends paid on common stock													(5,067)	(5,426)	(5,921)
Issuance of common stock due to restricted stock													3	1	1
Repurchases of common stock													(86,853)	(120,437)	(168,235)
Net cash provided by (used in) financing activities													(443,200)	604,858	117,818
Net change in cash and cash equivalents													(217,243)	(12,458)	74,019
Cash and cash equivalents at beginning of fiscal year				375,580				388,038				314,019	375,580	388,038	314,019
Cash and cash equivalents at end of fiscal period	158,337				375,580				388,038				158,337	375,580	388,038
Meta Financial
Cash flows from operating activities:
Net income attributable to parent													168,357	163,615	156,386
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation, amortization and accretion, net													102	102	1,020
Equity in undistributed net income of subsidiaries													(172,017)	(166,738)	(159,652)
Net change in accrued interest receivable													46	(30)	(15)
Net change in other assets													(997)	(354)	(636)
Net change in accrued expenses and other liabilities													1,315	(1,793)	3,163
Cash dividend received													87,000	110,000	229,200
Stock compensation													10,287	11,070	10,004
Net cash provided by operating activities													94,093	115,872	239,470
Cash flows from investing activities:
Alternative investments													(1,676)	(1,217)	(3,380)
Net cash (used in) investing activities													(1,676)	(1,217)	(3,380)
Cash flows from financing activities:
Redemption of long-term borrowings													0	0	(75,000)
Payment of debt issuance costs													0	(511)	0
Proceeds from long-term borrowings													0	0	20,000
Dividends paid on common stock													(5,067)	(5,426)	(5,921)
Issuance of common stock due to restricted stock													2	1	1
Issuance of common stock due to ESOP													0	0	2,886
Repurchases of common stock													(86,853)	(120,437)	(168,235)
Net cash provided by (used in) financing activities													(91,918)	(126,373)	(226,269)
Net change in cash and cash equivalents													499	(11,718)	9,821
Cash and cash equivalents at beginning of fiscal year				$ 1,399				$ 13,117				$ 3,296	1,399	13,117	3,296
Cash and cash equivalents at end of fiscal period	$ 1,898				$ 1,399				$ 13,117				$ 1,898	$ 1,399	$ 13,117