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Business - Additional Information (Detail)
$ in Millions
Sep. 22, 2016
USD ($)
Branch
Feb. 29, 2016
USD ($)
Branch
Dec. 31, 2016
Location
Subsidiary
Schedule Of Description Of Company [Line Items]      
Number of inactive subsidiaries | Subsidiary     1
Bank operated Business Financial Centers, number     42
Bank operated Commercial Banking Centers, number     8
Bank operated trust office locations, number     3
County Commerce Bank [Member]      
Schedule Of Description Of Company [Line Items]      
Total assets of acquired/merger company | $   $ 253  
Number of bank branches acquired | Branch   4  
Valley Business Bank [Member]      
Schedule Of Description Of Company [Line Items]      
Total assets of acquired/merger company | $ $ 416    
Number of bank branches acquired | Branch 4