Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Securities held to maturity, fair value	$ 466,060	$ 473,753
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	41,292,045
Common stock, shares outstanding	40,373,753	40,293,291