Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Securities held to maturity, fair value	$ 381,950	$ 473,753
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (shares)	5,000,000	5,000,000
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Common stock, par value (usd per share)	$ 5.00	$ 5.00
Common stock, shares authorized (shares)	150,000,000	150,000,000
Common stock, shares issued (shares)	42,972,066	41,292,045
Common stock, shares outstanding (shares)	42,102,224	40,293,291