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Regulatory Matters - Additional Information (Detail) - USD ($)
$ in Millions
 12 Months Ended
Jan. 01, 2016
Dec. 31, 2016
Dec. 31, 2015
Regulated Operations [Abstract]      
Capital conservation buffer rate 0.625%    
Capital conservation buffer phase period   4 years  
Capital conservation buffer rate, full implementation   2.50%  
Percentage of required capital conservation buffer rate of CET1   2.50%  
Capital conservation buffer phase in beginning period   Jan. 01, 2016  
Capital conservation buffer phase in end period   Jan. 01, 2019  
Trust-preferred securities included in Tier 1 capital   $ 25.0 $ 25.0
Additional dividends without obtaining prior approval from bank regulators declared and paid   $ 174.6