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Business - Additional Information (Detail) $ in Millions	Mar. 31, 2016 FinancialCenters Subsidiary	Feb. 29, 2016 USD ($) Branch
Schedule Of Description Of Company [Line Items]
Number of inactive subsidiaries \| Subsidiary	1
Bank operated Business Financial Centers, number	44
Bank operated Commercial Banking Centers, number	8
Bank operated trust offices, number	3
County Commerce Bank [Member]
Schedule Of Description Of Company [Line Items]
Total assets of merger company \| $		$ 253
Number of branches owned by merger company \| Branch		4