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Securities - Additional Information (Detail)
 3 Months Ended 12 Months Ended
Mar. 31, 2017
USD ($)
Securities
Dec. 31, 2016
Securities
Schedule of Available-for-sale Securities [Line Items]    
Percentage of investment portfolio 100.00% 100.00%
Weighted-average period of re-pricing of portfolio 4 years 6 months 4 years 8 months 12 days
Impairment recognized | $ $ 0  
U.S. Agency and Mortgage-Backed Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Number of securities in an unrealized loss position 54 64
Total number of securities 83 83
Obligations of States and Political Subdivisions [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Number of securities in an unrealized loss position 33 50
Total number of securities 78 78
Corporate Debt Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Number of securities in an unrealized loss position 1 1