Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Securities held to maturity, fair value	$ 490,233	$ 442,488
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (usd per share)	$ 5.00	$ 5.00
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	41,292,045	32,656,166
Common stock, shares outstanding	40,268,455	31,545,145