Business Combinations - Consideration, Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands			6 Months Ended
	Jun. 30, 2015	Mar. 04, 2015	Jun. 30, 2015	Dec. 31, 2014
Fair Value of Liabilities Assumed
Goodwill	$ 291,204		$ 291,204	$ 175,820
Integrity Bancshares, Inc. [Member]
Business Acquisition [Line Items]
Cash		$ 29,500	29,510
Common stock	142,469		142,469
Fair value of total consideration	171,979	172,000
Fair Value of Assets Acquired
Cash and cash equivalents	13,163		13,163
Securities and other investments	11,502		11,502
Loans	788,687	788,700	788,687
Bank owned life insurance	15,974		15,974
Premises and equipment	10,855		10,855
Core deposit intangible	5,713		5,713
Other assets	19,555		19,555
Total Assets Acquired	865,449		865,449
Fair Value of Liabilities Assumed
Deposits	722,308		722,308
Borrowings	82,286		82,286
Other liabilities	4,259		4,259
Total Liabilities Assumed	808,853		808,853
Total Fair Value of Identifiable Net Assets	56,596		56,596
Goodwill	$ 115,383	$ 115,400	$ 115,383