Business Combinations - Pro Forma Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Business Acquisition [Line Items]
Net interest income	$ 40,259us-gaap_InterestIncomeExpenseNet	$ 35,591us-gaap_InterestIncomeExpenseNet
Net income	12,835us-gaap_NetIncomeLoss	14,033us-gaap_NetIncomeLoss
Integrity Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Net interest income	2,200
Net income	300
Business Acquisition, Pro Forma Information [Abstract]
Total revenue	58,208	53,996
Net income (1)	$ 14,502	$ 16,052
Earnings per common share: (1)
Basic (in USD per share)	$ 0.42	$ 0.46
Diluted (in USD per share)	$ 0.42	$ 0.46

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The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

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The net amount of operating interest income (expense).

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