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Goodwill and Other Intangible Assets - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Goodwill And Other Intangible Assets [Line Items]      
Carrying amount of goodwill $ 621,193,000 $ 621,193,000  
Percentage of fair market value of goodwill higher than book value, weighted approach 15.00%    
Goodwill impairment $ 0 $ 0 $ 0
Intangible assets written off related to the sale of business unit $ 1,100,000    
Core Deposit Intangibles [Member]      
Goodwill And Other Intangible Assets [Line Items]      
Weighted-average remaining life of intangible assets 10 years    
Other Identifiable Intangibles [Member]      
Goodwill And Other Intangible Assets [Line Items]      
Weighted-average remaining life of intangible assets 8 years