Business Combinations - Pro Forma Information (Details) - Integrity Bancshares, Inc. [Member] - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Business Acquisition, Pro Forma Information [Abstract]
Total revenue	[1]	$ 59,819	$ 58,875	$ 179,559	$ 174,097
Net income	[2]	$ 18,527	$ 18,250	$ 51,406	$ 51,651
Earnings per common share:
Basic (in USD per share)	[2]	$ 0.53	$ 0.53	$ 1.49	$ 1.49
Diluted (in USD per share)	[2]	$ 0.53	$ 0.53	$ 1.48	$ 1.49

[1] Total pro forma revenue is defined as net interest income plus non-interest income, excluding gains and losses on sales of investment securities available-for-sale.

[2] Excludes merger expenses