Quarterly report [Sections 13 or 15(d)]

Borrowings and Subordinated Debentures - Additional Information (Detail)

v3.26.1
Borrowings and Subordinated Debentures - Additional Information (Detail) - USD ($)
 1 Months Ended 3 Months Ended 12 Months Ended
Aug. 20, 2021
Dec. 31, 2005
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Dec. 31, 2014
Debt Instrument [Line Items]            
Interest expense on borrowings     $ 676,000 $ 2,024,000    
Pledged loans, carrying value     2,260,000,000   $ 2,400,000,000  
Total borrowing capacity available from the collateral     1,660,000,000   1,760,000,000  
Remaining available borrowing capacity     1,510,000,000   1,460,000,000  
Average balance of FHLB advances     68,944,000   82,390,000  
Borrowing capacity through Fed Discount Window     411,800,000   424,500,000  
Interest expense on FHLB     700,000 2,000,000    
Debt instrument, maturity date Sep. 01, 2031          
FHLB of San Francisco            
Debt Instrument [Line Items]            
Pledged loans, carrying value     515,700,000   528,100,000  
2031 Notes            
Debt Instrument [Line Items]            
Subordinated debentures issued $ 110,000,000          
Fixed interest rate 3.75%          
Amortization of debt issuance costs $ 2,100,000          
Debt issuance costs, net     $ 108,800,000   108,700,000  
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% 5.34%      
Debt outstanding, net of issuance cost     $ 22,600,000   22,500,000  
Unpaid principal balance           $ 26,800,000
Estimated fair value           18,500,000
Debt instrument discount     $ 4,200,000   $ 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    
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%