Annual report pursuant to Section 13 and 15(d)

Loans - Additional Information (Details)

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Loans - Additional Information (Details) - USD ($)
6 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Accounts Notes And Loans Receivable [Line Items]        
Pledged loans, collateral for FHLB advances   $ 927,300,000 $ 668,500,000  
Pledged loans, collateral under PPPLF   149,800,000 0  
Amount outstanding [1]   2,388,532,000 1,767,182,000  
Unfunded commitments to related parties   312,683,000 244,800,000  
Executive Officers and Directors        
Accounts Notes And Loans Receivable [Line Items]        
Unfunded commitments to related parties   1,800,000 861,000  
Consumer Mortgage Loans        
Accounts Notes And Loans Receivable [Line Items]        
Recorded mortgage loans in process of foreclosure   0 0  
SBA Loans        
Accounts Notes And Loans Receivable [Line Items]        
Paycheck protection program loans under CARES Act   430,800,000    
Paycheck protection program loans forgiven amount   $ 153,000,000.0    
PPP loan interest rate   1.00%    
Deferred origination costs   $ 4,900,000    
Deferred origination fees   $ 15,300,000    
Weighted average life of debt   1 year 3 months 18 days    
Amount outstanding   $ 149,800,000    
Interest rate   0.35%    
Unpaid principal balances of loans serviced   $ 193,300,000 205,000,000.0  
Loan expenses   1,200,000 929,000 $ 2,700,000
SBA Loans | Director        
Accounts Notes And Loans Receivable [Line Items]        
Servicing loans sold $ 1,500,000      
Realized gains on servicing loans sold $ 0      
SBA Loans | Third Party        
Accounts Notes And Loans Receivable [Line Items]        
Servicing loans sold   21,100,000 47,800,000 69,000,000.0
Realized gains on servicing loans sold   1,800,000 $ 4,000,000.0 $ 5,100,000
SBA Loans | Loan Forgiveness and Normal Amortization        
Accounts Notes And Loans Receivable [Line Items]        
Origination fees net of costs   7,100,000    
Remaining origination fees net of costs   $ 3,300,000    
SBA Loans | Minimum        
Accounts Notes And Loans Receivable [Line Items]        
Paycheck protection program loans contractual term   2 years    
SBA Loans | Maximum        
Accounts Notes And Loans Receivable [Line Items]        
Paycheck protection program loans contractual term   5 years    
SBA Loans | Commercial and Industrial Loans        
Accounts Notes And Loans Receivable [Line Items]        
Paycheck protection program loans under CARES Act   $ 277,800,000    
Federal Reserve Bank Of Boston Special Purpose Vehicle | Main Street Lending Program        
Accounts Notes And Loans Receivable [Line Items]        
Servicing loans sold   400,300,000    
Realized gains on servicing loans sold   3,600,000    
Unpaid principal balances of loans serviced   $ 400,300,000    
Percentage of loan balance purchased   95.00%    
[1] Balance includes $(8.2) million and $(4.2) million of deferred fees, cost, premium and discount as of December 31, 2020 and 2019, respectively.