Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Securities held to maturity, fair value	$ 1,526,040	$ 1,468,258
Unearned income on loans	$ 49,856	$ 56,131
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	20,000,000	20,000,000
Preferred stock, shares issued	110,877	110,877
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	176,434,735	175,450,303
Treasury stock, shares	1,147,755	1,458,045