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Goodwill and Intangible Assets - Additional Information (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Sep. 14, 2018
Acquired Finite Lived Intangible Assets [Line Items]        
Goodwill $ 76,851 $ 27,095    
Amortization of core deposit intangible assets 366 586 $ 699  
Aggregate mortgage servicing rights amortization $ 126 72 $ 74  
UCB [Member]        
Acquired Finite Lived Intangible Assets [Line Items]        
Goodwill       $ 49,756
Increased in carrying amount of goodwill   $ 49,756