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Available for Sale Debt Securities - Additional Information (Detail)
12 Months Ended
Dec. 31, 2019
USD ($)
security
Dec. 31, 2018
USD ($)
security
shares
Dec. 31, 2017
USD ($)
Debt Securities, Available-for-sale [Line Items]      
Securities available for sale at carrying value $ 536,400,000 $ 524,200,000  
Amortized cost 965,135,000 1,076,282,000  
Fair value 976,919,000 $ 1,063,079,000  
Available for sale securities sold (in shares) | shares   15,046  
Proceeds from sales of available for sale debt securities $ 0 $ 2,212,000 $ 0
Number of securities in an unrealized loss position | security 50 175  
Mortgage-backed securities      
Debt Securities, Available-for-sale [Line Items]      
Amortized cost $ 936,196,000 $ 1,048,415,000  
Fair value 947,430,000 1,034,969,000  
Private Label Mortgage-Backed Securities      
Debt Securities, Available-for-sale [Line Items]      
Amortized cost $ 17,000    
Number of securities in an unrealized loss position | security 1    
Unrealized losses $ 1,000    
Available-for-sale Securities      
Debt Securities, Available-for-sale [Line Items]      
Amortized cost 28,939,000    
Fair value $ 29,489,000    
Proceeds from sales of available for sale debt securities   $ 2,200,000 $ 0