LOANS & ALLOWANCE FOR CREDIT LOSSES - NARRATIVE (Details)	12 Months Ended
Jun. 30, 2023 USD ($) segment	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)
Financing Receivable, Impaired [Line Items]
Number of loan portfolio segments \| segment	6
Accrued interest receivable	$ 77,900,000	$ 50,100,000
Financing Receivable, Accrued Interest, after Allowance for Credit Loss, Statement of Financial Position [Extensible Enumeration]	Other assets	Other assets
Advances, collateral pledged	$ 5,128,400,000	$ 3,823,100,000
FRBSF and FRB, loans pledged	3,689,500,000	3,861,600,000
Purchased loans serviced by others, amount	$ 32,500,000	$ 37,300,000
Purchased loans serviced by others, percent	0.20%	0.26%
Nonaccrual loans, without an allowance	$ 0	$ 0
Interest recognized on performing loans temporarily modified as TDRs	0	0	$ 0
Interest income recognized	0	0	0
Loans past due ninety days or more and still accruing	14,000,000	0
Mortgage loans in process of foreclosure, amount	$ 22,200,000	$ 20,700,000
Nonaccrual
Financing Receivable, Impaired [Line Items]
Ratio of nonaccrual loans and leases considered TDRs	1.77%	1.18%
Performing
Financing Receivable, Impaired [Line Items]
Amount in performing TDRs	$ 0	$ 0	$ 0
Single Family - Mortgage & Warehouse
Financing Receivable, Impaired [Line Items]
Interest only loans	1,331,200,000	1,197,400,000
Option adjustable-rate mortgage loans	$ 8,900,000	$ 7,000,000
Single Family - Mortgage & Warehouse \| California \| Financing Receivable \| Geographic concentration risk
Financing Receivable, Impaired [Line Items]
Concentration risk percentage	71.40%	70.60%
Single Family - Mortgage & Warehouse \| New York \| Financing Receivable \| Geographic concentration risk
Financing Receivable, Impaired [Line Items]
Concentration risk percentage	11.00%	13.00%
Multifamily Loan Category \| California \| Financing Receivable \| Geographic concentration risk
Financing Receivable, Impaired [Line Items]
Concentration risk percentage	69.10%	68.30%
Multifamily Loan Category \| New York \| Financing Receivable \| Geographic concentration risk
Financing Receivable, Impaired [Line Items]
Concentration risk percentage	19.70%	18.80%
Commercial Real Estate \| California \| Financing Receivable \| Geographic concentration risk
Financing Receivable, Impaired [Line Items]
Concentration risk percentage		11.90%
Commercial Real Estate \| New York \| Financing Receivable \| Geographic concentration risk
Financing Receivable, Impaired [Line Items]
Concentration risk percentage	37.50%	40.50%
Commercial Real Estate \| FLORIDA \| Financing Receivable \| Geographic concentration risk
Financing Receivable, Impaired [Line Items]
Concentration risk percentage	10.50%
Fixed Interest Rate
Financing Receivable, Impaired [Line Items]
Percent of loans by interest rate type	7.00%	9.00%
Adjustable Interest Rate
Financing Receivable, Impaired [Line Items]
Percent of loans by interest rate type	93.00%	91.00%

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Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

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