CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
CONSOLIDATED BALANCE SHEETS
Securities available-for-sale, cost (in dollars)	$ 5,894,509	$ 6,267,691
Securities held-to-maturity, fair value (in dollars)	3,484,647	2,883,935
Other real estate owned, covered by FDIC loss share (in dollars)	$ 12,760	$ 25,481
Preferred stock, par value (in dollars per share)	$ 1.00	$ 1.00
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	275,000	275,000
Common stock, par value (in dollars per share)	$ 1.00	$ 1.00
Common stock, shares authorized	75,000,000	75,000,000
Common stock, shares issued	55,162,455	54,667,295
Treasury shares	377,224	483,523