CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
CONSOLIDATED BALANCE SHEETS
Securities available-for-sale, cost (in dollars)	$ 5,201,001	$ 5,894,509
Securities held-to-maturity, fair value (in dollars)	3,510,553	3,484,647
Other real estate owned, covered by FDIC loss share (in dollars)	$ 11,552	$ 12,760
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	55,510,321	55,162,455
Treasury shares	313,965	377,224