Fair Value Measurements - Narrative (Details) - USD ($)		9 Months Ended
	Mar. 01, 2024	Jun. 30, 2024	Jun. 30, 2023	Sep. 30, 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Available-for-sale securities purchased		$ 321,308,000	$ 317,027,000
Proceeds from sales of available-for-sale securities		179,215,000	94,000
Held-to-maturity securities purchased		47,092,000	0
Proceeds from sale of held-to-maturity securities		$ 0	$ 0
Term of contractual due dates, mortgage-backed securities		25 years
Accrued interest for available-for-sale securities		$ 9,772,000		$ 8,641,000
Accrued interest for held-to-maturity securities		1,181,000		$ 1,013,000
Luther Burbank
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Acquisition, investments purchased, AFS securities	$ 516,308,000
Acquisition, investments sold, AFS securities	171,000,000
Acquisition, investments purchased, HTM securities	$ 2,570,000
Consumer loans | Single-family residential
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Foreclosed residential real estate properties held as REO		28,000
Real estate acquired through foreclosure		$ 6,134,000