Parent Company Financial Statements (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets
Investment securities	$ 6,861,293,000	$ 7,171,917,000
Other assets	417,391,000	394,027,000
Total assets	31,475,934,000	30,075,113,000
Liabilities and Shareholders' Equity
Short-term borrowings	594,733,000	987,184,000
Long-term obligations	704,155,000	351,320,000
Other liabilities	247,729,000	253,903,000
Stockholders' equity	2,872,109,000	2,687,594,000	$ 2,071,462,000	$ 1,859,624,000
Total liabilities and shareholders' equity	31,475,934,000	30,075,113,000
Income Statement [Abstract]
Interest expense	44,304,000	50,351,000	56,618,000
Net interest income (loss)	924,905,000	710,097,000	740,186,000
Income tax benefit	122,028,000	65,032,000	101,574,000
Net income	210,386,000	138,562,000	166,869,000
OPERATING ACTIVITIES
Net income	210,386,000	138,562,000	166,869,000
Net amortization of premiums and accretion of discounts	(85,066,000)	(48,374,000)	(112,759,000)
Gain on elimination of acquired debt	0	(1,988,000)	0
Securities (gains) losses	(10,817,000)	(29,096,000)	0
Gain on sale of other assets	0	0	(4,085,000)
Other than temporary impairment on securities	0
Change in other assets	(12,904,000)	(72,680,000)	100,437,000
Change in other liabilities	14,458,000	1,319,000	49,177,000
INVESTING ACTIVITIES
Net change in short-term borrowings	(397,952,000)	(25,321,000)	(57,087,000)
Retirement of long-term obligations	(5,896,000)	(54,301,000)	(4,152,000)
Stock issuance costs	0	(619,000)	0
Repurchase of common stock	0	0	(321,000)
Cash dividends paid	(18,015,000)	(11,543,000)	(8,663,000)
Net change in cash	(70,096,000)	70,583,000	(106,131,000)
Cash and due from banks at beginning of period	604,182,000	533,599,000	639,730,000
Cash and due from banks at end of period	534,086,000	604,182,000	533,599,000
Cash payments for
Interest	46,785,000	48,894,000	59,234,000
Income taxes	136,900,000	127,970,000	102,890,000
Parent
Assets
Cash	26,285,000	24,026,000
Investment securities	21,137,000	110,644,000
Investment in Banking Subsidiaries	2,874,581,000	2,750,201,000
Investment in Other Subsidiaries	43,117,000	65,665,000
Due from subsidiaries	0	295,994,000
Other assets	73,944,000	74,157,000
Total assets	3,039,064,000	3,320,687,000
Liabilities and Shareholders' Equity
Short-term borrowings	0	485,207,000
Long-term obligations	133,775,000	136,717,000
Due to Affiliate	29,682,000	0
Other liabilities	3,498,000	11,169,000
Stockholders' equity	2,872,109,000	2,687,594,000
Total liabilities and shareholders' equity	3,039,064,000	3,320,687,000
Income Statement [Abstract]
Interest income	645,000	1,784,000	1,387,000
Interest expense	6,793,000	9,694,000	7,065,000
Net interest income (loss)	(6,148,000)	(7,910,000)	(5,678,000)
Dividend Income, Banking Subsidiaries	75,006,000	82,419,000	131,006,000
Dividends from subsidiaries	23,500,000	0	0
Other income (loss)	1,870,000	33,600,000	3,620,000
Other operating expense	2,634,000	6,534,000	2,344,000
Income before income tax benefit and equity in undistributed net income of subsidiaries	91,594,000	101,575,000	126,604,000
Income tax benefit	(2,618,000)	(2,590,000)	(2,095,000)
Income before equity in undistributed net income of subsidiaries	94,212,000	104,165,000	128,699,000
Excess distributions (undistributed ) net income of subsidiaries	(116,174,000)	(34,397,000)	(38,170,000)
Net income	210,386,000	138,562,000	166,869,000
OPERATING ACTIVITIES
Net income	210,386,000	138,562,000	166,869,000
Excess distributions (undistributed ) net income of subsidiaries	(116,174,000)	(34,397,000)	(38,170,000)
Net amortization of premiums and accretion of discounts	(2,712,000)	594,000	334,000
Gain on elimination of acquired debt	0	(1,988,000)	0
Securities (gains) losses	(236,000)	(29,126,000)	0
Gain on sale of other assets	0	0	(1,331,000)
Change in other assets	(3,070,000)	93,385,000	(61,704,000)
Change in other liabilities	(1,157,000)	2,250,000	(2,096,000)
Net cash provided by (Used in) Operating Activities	87,037,000	169,280,000	63,902,000
INVESTING ACTIVITIES
Net change in due from subsidiaries	295,994,000	(150,328,000)	(67,154,000)
Purchases of investment securities	(7,818,000)	(33,243,000)	(126,197,000)
Maturities and sales of investment securities	100,586,000	114,208,000	135,000,000
Investment in subsidiaries	0	1,579,000	1,489,000
Business acquisitions, net of cash acquired	0	(24,772,000)	0
Net Cash Provided by (Used in) Investing Activities	388,762,000	(92,556,000)	(56,862,000)
Change in Due to Subsidiaries	29,682,000	0	0
Net change in short-term borrowings	(485,207,000)	(1,211,000)	12,860,000
Retirement of long-term obligations	0	(52,372,000)	0
Stock issuance costs	0	(619,000)	0
Repurchase of common stock	0	0	(321,000)
Cash dividends paid	(18,015,000)	(11,543,000)	(8,663,000)
Net cash used by financing activities	(473,540,000)	(65,745,000)	3,876,000
Net change in cash	2,259,000	10,979,000	10,916,000
Cash and due from banks at beginning of period	24,026,000	13,047,000	2,131,000
Cash and due from banks at end of period	$ 26,285,000	$ 24,026,000	$ 13,047,000