Parent Company Financial Statements (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Assets
Investment securities	$ 5,387,703,000	$ 5,226,228,000
Other assets	263,797,000	367,610,000
Total assets	21,199,091,000	21,283,652,000
Liabilities and Shareholders' Equity
Short-term borrowings	511,418,000	568,505,000
Long-term obligations	510,769,000	444,921,000
Other liabilities	116,785,000	218,553,000
Stockholders' equity	2,076,675,000	1,864,007,000	1,861,128,000	1,732,962,000
Total liabilities and shareholders' equity	21,199,091,000	21,283,652,000
Income Statement [Abstract]
Interest expense	56,618,000	90,148,000	144,192,000
Net interest income (loss)	740,186,000	914,688,000	870,967,000
Income tax benefit	96,965,000	59,822,000	115,103,000
Net income	167,699,000	134,348,000	195,028,000
OPERATING ACTIVITIES
Net income	167,699,000	134,348,000	195,028,000
Net amortization of premiums and accretion of discounts	(115,060,000)	(158,227,000)	(194,434,000)
Gain on retirement of long-term obligations	0	0	(9,685,000)
Securities (gains) losses	0	(2,277,000)	288,000
Gain on sale of other assets	(4,085,000)	0	0
Other than temporary impairment on securities	0
Change in other assets	103,974,000	(17,617,000)	89,979,000
Change in other liabilities	56,998,000	23,967,000	(1,541,000)
INVESTING ACTIVITIES
Net change in short-term borrowings	(57,087,000)	(101,717,000)	(283,440,000)
Retirement of long-term obligations	(4,152,000)	(196,338,000)	(320,730,000)
Repurchase of common stock	(321,000)	(103,624,000)	(24,387,000)
Cash dividends paid	(8,663,000)	(15,398,000)	(12,499,000)
Net change in cash	(106,131,000)	48,929,000	130,623,000
Cash and due from banks at beginning of period	639,730,000	590,801,000	460,178,000
Cash and due from banks at end of period	533,599,000	639,730,000	590,801,000
Cash payments for
Interest	59,234,000	104,514,000	157,477,000
Income taxes	102,890,000	66,453,000	91,465,000
Parent [Member]
Assets
Cash	13,047,000	2,131,000
Investment securities	234,488,000	237,765,000
Investment in subsidiaries	2,058,505,000	1,969,600,000
Due from subsidiaries	145,666,000	78,512,000
Other assets	144,998,000	83,283,000
Total assets	2,596,704,000	2,371,291,000
Liabilities and Shareholders' Equity
Short-term borrowings	411,907,000	399,047,000
Long-term obligations	96,392,000	96,392,000
Other liabilities	11,730,000	11,845,000
Stockholders' equity	2,076,675,000	1,864,007,000
Total liabilities and shareholders' equity	2,596,704,000	2,371,291,000
Income Statement [Abstract]
Interest income	1,387,000	1,353,000	1,345,000
Interest expense	7,065,000	15,435,000	21,512,000
Net interest income (loss)	(5,678,000)	(14,082,000)	(20,167,000)
Dividends from subsidiaries	131,006,000	179,588,000	82,812,000
Other income (loss)	3,620,000	2,843,000	9,699,000
Other operating expense	2,344,000	6,384,000	5,298,000
Income before income tax benefit and equity in undistributed net income of subsidiaries	126,604,000	161,965,000	67,046,000
Income tax benefit	(2,095,000)	(8,417,000)	(5,531,000)
Income before equity in undistributed net income of subsidiaries	128,699,000	170,382,000	72,577,000
(Excess distributions) equity in undistributed net income of subsidiaries	39,000,000	(36,034,000)	122,451,000
Net income	167,699,000	134,348,000	195,028,000
OPERATING ACTIVITIES
Net income	167,699,000	134,348,000	195,028,000
Undistributed net income of subsidiaries	(39,000,000)	36,034,000	(122,451,000)
Net amortization of premiums and accretion of discounts	334,000	439,000	203,000
Gain on retirement of long-term obligations	0	0	(9,685,000)
Securities (gains) losses	0	(2,274,000)	(62,000)
Gain on sale of other assets	(1,331,000)	0	0
Other than temporary impairment on securities	0	45,000	26,000
Change in other assets	(61,704,000)	30,761,000	(20,951,000)
Change in other liabilities	(2,096,000)	(10,148,000)	(1,925,000)
Net cash provided by (Used in) Operating Activities	63,902,000	189,205,000	40,183,000
INVESTING ACTIVITIES
Net change in due from subsidiaries	(67,154,000)	42,323,000	146,463,000
Purchases of investment securities	(126,197,000)	(111,409,000)	(220,387,000)
Maturities and sales of investment securities	135,000,000	112,625,000	75,151,000
Investment in subsidiaries	1,489,000	9,298,000	0
Net Cash Provided by (Used in) Investing Activities	(56,862,000)	52,837,000	1,227,000
Net change in short-term borrowings	12,860,000	23,651,000	4,046,000
Retirement of long-term obligations	0	(155,305,000)	(11,815,000)
Repurchase of common stock	(321,000)	(103,624,000)	(24,387,000)
Cash dividends paid	(8,663,000)	(15,398,000)	(12,499,000)
Net cash used by financing activities	3,876,000	(250,676,000)	(44,655,000)
Net change in cash	10,916,000	(8,634,000)	(3,245,000)
Cash and due from banks at beginning of period	2,131,000	10,765,000	14,010,000
Cash and due from banks at end of period	13,047,000	2,131,000	10,765,000
Cash payments for
Interest	6,904,000	25,574,000	20,677,000
Income taxes	$ 102,890,000	$ 66,453,000	$ 91,465,000