v3.26.1
Borrowings and Subordinated Debentures - Additional Information (Detail) - USD ($)
 1 Months Ended 3 Months Ended 6 Months Ended 12 Months Ended
Jul. 30, 2026
Aug. 20, 2021
Dec. 31, 2005
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Dec. 31, 2014
Debt Instrument [Line Items]                  
Interest expense on borrowings       $ 154,000 $ 684,000 $ 830,000 $ 2,708,000    
Pledged loans, carrying value       2,200,000,000   2,200,000,000   $ 2,400,000,000  
Total borrowing capacity available from the collateral       1,620,000,000   1,620,000,000   1,760,000,000  
Borrowing capacity reduced by amount in Federal Home Loan Bank letters of credit       180,000,000   180,000,000   150,000,000  
Remaining available borrowing capacity       1,440,000,000   1,440,000,000   1,460,000,000  
Average balance of FHLB advances           41,851,000   82,390,000  
Borrowing capacity through Fed Discount Window       858,000,000   858,000,000   424,500,000  
Interest expense on FHLB       100,000 700,000 800,000 2,700,000    
Debt instrument, maturity date Jul. 31, 2036 Sep. 01, 2031              
FHLB of San Francisco                  
Debt Instrument [Line Items]                  
Pledged loans, carrying value       1,220,000,000   1,220,000,000   528,100,000  
2031 Notes                  
Debt Instrument [Line Items]                  
Subordinated debentures issued $ 55,000,000 $ 110,000,000              
Fixed interest rate 6.50% 3.75%              
Amortization of debt issuance costs   $ 2,100,000              
Debt issuance costs, net       108,800,000   108,800,000   108,700,000  
Subordinated debentures                  
Debt Instrument [Line Items]                  
Debt instrument discount       $ 21,900,000   $ 21,900,000   21,700,000  
Subordinated debentures | Central Bancorp, Inc                  
Debt Instrument [Line Items]                  
Subordinated debentures issued     $ 26,000,000            
Debt instrument, maturity date           Mar. 15, 2036      
Fixed interest rate     6.26% 5.33%   5.33%      
Debt outstanding, net of issuance cost       $ 22,700,000   $ 22,700,000   22,500,000  
Unpaid principal balance                 $ 26,800,000
Estimated fair value                 18,500,000
Debt instrument discount       4,100,000   $ 4,100,000   $ 4,300,000 $ 8,300,000
Frequency of interest payment           quarterly      
Term for the initial fixed interest rate           5 years      
Optional interest payment deferral period (not to exceed)           5 years      
Variable interest rate basis           three-month LIBOR plus 140 basis points      
Amortization of subordinated debentures       104,000,000 $ 112,000,000 $ 208,000,000 $ 224,000,000    
TPS                  
Debt Instrument [Line Items]                  
Investments       $ 800,000   $ 800,000      
Benchmark Rate | 2031 Notes                  
Debt Instrument [Line Items]                  
Basis spread   3.10%              
3-month London Interbank Offered Rate (LIBOR) | Subordinated debentures | Central Bancorp, Inc                  
Debt Instrument [Line Items]                  
Basis spread     1.40%            
Three Month Secured Overnight Financing Rate (SOFR ) | Subordinated debentures | Central Bancorp, Inc                  
Debt Instrument [Line Items]                  
Basis spread           1.66%      
Three Month Secured Overnight Financing Rate (SOFR ) | Credit Spread | Subordinated debentures | Central Bancorp, Inc                  
Debt Instrument [Line Items]                  
Basis spread           1.40%      
Three Month Secured Overnight Financing Rate (SOFR ) | Adjustment to Convert 3-month LIBOR to 3-month SOFR | Subordinated debentures | Central Bancorp, Inc                  
Debt Instrument [Line Items]                  
Basis spread           0.26%