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Borrowings - Additional Information (Detail) - USD ($)
12 Months Ended
Mar. 13, 2017
Dec. 31, 2019
Dec. 31, 2018
Mar. 12, 2018
Debt Instrument [Line Items]        
Drawing against Federal Home Loan Bank advances   $ 324,373,000 $ 384,898,000  
Line of credit facility maximum borrowing capacity $ 30,000,000     $ 40,000,000
Debt Instrument, Maturity Date   May 15, 2020    
Debt Instrument, Term 5 years      
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage 0.20%      
Federal Home Loan Bank Line of Credit Advances [Member]        
Debt Instrument [Line Items]        
Drawing against Federal Home Loan Bank advances   $ 311,223,000 $ 368,770,000  
Weighted average interest rate on drawings   1.79% 2.65%  
Federal Home Loan Bank Advances [Member]        
Debt Instrument [Line Items]        
Letter of credit   $ 38,500,000 $ 31,451,000  
Line of credit facility maximum borrowing capacity   811,394,000 951,196,000  
Line of credit facility additional borrowing capacity   448,278,000 534,627,000  
Residential Mortgage-Backed Securities (Issued by Government-Sponsored Entities) [Member]        
Debt Instrument [Line Items]        
Residential mortgage-backed securities, fair value   $ 40,412,000 $ 51,701,000