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Derivatives - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Derivatives Fair Value [Line Items]      
Swap fees $ 1,459,000 $ 516,000 $ 621,000
Collateral Pledged [Member] | Interest Rate Swap [Member]      
Derivatives Fair Value [Line Items]      
Cash and securities at fair value pledged for collateral 11,705,000 $ 14,032,000  
Cash and Cash Equivalents [Member] | Interest Rate Swap [Member]      
Derivatives Fair Value [Line Items]      
Cash and securities at fair value pledged for collateral $ 11,300,000