Annual report pursuant to Section 13 and 15(d)

Subordinated Debentures - Additional Information (Detail)

v3.22.0.1
Subordinated Debentures - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
Aug. 20, 2021
Mar. 21, 2017
Dec. 31, 2005
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2014
Debt Instrument [Line Items]              
Subordinated debentures issued       $ 224,100,000 $ 126,800,000    
Debt instrument, maturity date Sep. 01, 2031 Mar. 30, 2027          
Debt issuance cost $ 2,100            
2021 Notes              
Debt Instrument [Line Items]              
Subordinated debentures issued $ 110,000,000.0            
Fixed interest rate 3.75%            
Amortization of debt issuance costs       62,000      
Debt issuance costs, net       108,000,000.0      
2021 Notes | Benchmark Rate              
Debt Instrument [Line Items]              
Basis spread 3.10%            
2017 Notes              
Debt Instrument [Line Items]              
Subordinated debentures issued   $ 100,000,000.0          
Fixed interest rate   5.45%          
Debt issuance cost   $ 2,300,000          
Amortization of debt issuance costs       174,000      
Subordinated notes acquired       12,700,000      
Debt instrument, premium       343,000      
Incremental interest expense       517,000      
Debt outstanding, net of issuance cost       194,200,000 98,500,000    
2017 Notes | 3-month London Interbank Offered Rate (LIBOR)              
Debt Instrument [Line Items]              
Basis spread   3.315%          
Subordinated debentures              
Debt Instrument [Line Items]              
Amortization of debt issuance costs       $ 341,000 205,000 $ 193,000  
Subordinated debentures | Central Bancorp, Inc              
Debt Instrument [Line Items]              
Subordinated debentures issued     $ 26,000,000.0        
Debt instrument, maturity date       Mar. 15, 2036      
Fixed interest rate     6.26%        
Debt outstanding, net of issuance cost       $ 20,800,000 20,400,000    
Unpaid principal balance             $ 26,800,000
Estimated fair value             18,500,000
Debt instrument discount       $ 6,000,000.0 6,400,000   $ 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       $ 402,000 $ 390,000 $ 376,000  
Subordinated debentures | 3-month London Interbank Offered Rate (LIBOR) | Central Bancorp, Inc              
Debt Instrument [Line Items]              
Basis spread     140.00%