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Qualified Affordable Housing Project Investments - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Schedule Of Equity Method Investments [Line Items]          
Investment in qualified affordable housing projects $ 10,900,000   $ 10,900,000   $ 8,400,000
Unfunded commitments of investments in qualified affordable housing projects 8,500,000   8,500,000   $ 6,500,000
Recognized amortization expense included in income tax expense 180,000 $ 124,000 525,000 $ 367,000  
Recognized tax credits and other benefits from investment in affordable housing tax credits 207,000 141,000 601,000 418,000  
Impairment losses related to investment in qualified affordable housing projects $ 0 $ 0 $ 0 $ 0  
Minimum [Member]          
Schedule Of Equity Method Investments [Line Items]          
Expected period for fulfillment of investment commitments     8 years    
Maximum [Member]          
Schedule Of Equity Method Investments [Line Items]          
Expected period for fulfillment of investment commitments     10 years