Financial Information - WAFD, Inc.. - Statements of Cash Flows (Details) - USD ($) $ in Thousands		12 Months Ended
	Feb. 08, 2021	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Cash Flows From Operating Activities
Net income		$ 257,426	$ 236,330	$ 183,615
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense		7,914	6,808	6,381
Decrease (increase) in other assets		(67,342)	(100,146)	155,599
Net cash provided (used) by operating activities		213,957	268,465	314,454
Cash Flows From Investing Activities
Purchase of strategic investments		(12,500)	0	0
Net cash provided (used) by investing activities		(1,377,917)	(2,493,164)	(579,745)
Cash Flows From Financing Activities
Proceeds from exercise of common stock options and related tax benefit		1,089	1,823	339
Proceeds from issuance of preferred stock, net	$ 293,325	0	0	293,325
Proceeds from employee stock purchase		177	0	0
Treasury stock purchased		(30,463)	(3,260)	(348,651)
Dividends paid on preferred stock		(14,625)	(14,625)	(6,378)
Dividends on common stock		(63,792)	(61,576)	(65,876)
Net cash provided (used) by financing activities		1,460,644	817,855	653,123
Increase (decrease) in cash and cash equivalents		296,684	(1,406,844)	387,832
Cash at beginning of year		683,965
Cash at end of year		980,649	683,965
Parent Company
Cash Flows From Operating Activities
Net income		257,426	236,330	183,615
Adjustments to reconcile net income to net cash provided by operating activities:
Undistributed earnings from investments in subsidiaries		(202,643)	(63,956)	(91,697)
Distributions in excess of earnings from investments in subsidiaries		0	0	0
Stock-based compensation expense		7,914	6,808	6,381
Decrease (increase) in other assets		1,329	0	0
Increase in other liabilities		36	262	440
Net cash provided (used) by operating activities		64,062	179,444	98,739
Cash Flows From Investing Activities
Purchase of strategic investments		(12,500)	0	0
Net cash provided (used) by investing activities		(12,500)	0	0
Cash Flows From Financing Activities
Proceeds from exercise of common stock options and related tax benefit		1,089	1,823	339
Proceeds from issuance of preferred stock, net		0	0	293,325
Proceeds from employee stock purchase		177	0	0
Treasury stock purchased		(30,463)	(3,260)	(348,651)
Dividends paid on preferred stock		(14,625)	(14,625)	(6,378)
Dividends on common stock		(63,792)	(61,576)	(65,876)
Net cash provided (used) by financing activities		(107,614)	(77,638)	(127,241)
Increase (decrease) in cash and cash equivalents		(56,052)	101,806	(28,502)
Cash at beginning of year		130,502	28,696	57,198
Cash at end of year		$ 74,450	$ 130,502	$ 28,696