Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Value of equity interests (such as common shares, preferred shares, or partnership interest) issued or issuable to acquire the entity.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Total aggregate amount of all noninterest expense.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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Acquisitions - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended				3 Months Ended	9 Months Ended	12 Months Ended
Acquisitions - Additional Information (Detail) (USD $)	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 WNB Bancshares, Inc. [Member]	May 30, 2014 WNB Bancshares, Inc. [Member]	Sep. 30, 2014 Acquisition-related Costs [Member]	Sep. 30, 2014 Acquisition-related Costs [Member]	Dec. 31, 2013 Acquisition-related Costs [Member]
Business Acquisition [Line Items]
Preliminary purchase price allocation						$ 198,798,000
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned						149,700,000
Common stock number of shares issued for consideration					2,000,000
Amount of cash consideration					49,100,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life					10 years
Noninterest Expense	163,828,000	151,823,000	485,739,000	457,395,000			1,100,000	7,100,000	1,400,000
Other	$ 40,856,000	$ 36,886,000	$ 125,280,000	$ 115,744,000