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Secondary Market Mortgage Activities - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Debt Disclosure [Abstract]      
Total loans serviced to others $ 121,938,000 $ 107,165,000 $ 112,002,000
Fair value of mortgage servicing rights 1,391,000 964,000 896,000
Valuation allowance $ 0 $ 0 $ 0