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Securities - Additional Information (Detail)
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2016
USD ($)
Securities
Sep. 30, 2015
USD ($)
Sep. 30, 2016
USD ($)
Securities
Obligation
Security
Sep. 30, 2015
USD ($)
Dec. 31, 2015
Securities
Obligation
Amortized Cost and Fair Value Debt Securities [Abstract]          
Number of U.S. agency and mortgage-backed securities | Securities 7   7   52
Number of obligations of state and political subdivisions in an unrealized loss position | Obligation     0   13
Percentage of investment portfolio     100.00%   100.00%
Weighted-average period of re-pricing of portfolio     4 years   4 years 7 months 6 days
Gross gains or losses on held to maturity securities     $ 0    
Proceeds from sales of securities held to maturity $ 0 $ 0 $ 657,000 $ 0  
Held to maturity securities, number of securities sold | Security     1    
Impairment recognized     $ 0