Parent Company Information (Components of Condensed Cash Flow The Parent Company) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities:
Stock-based compensation	$ 10,935	$ 10,223	$ 10,664
Net cash provided by operating activities	307,185	272,815	463,953
Investing activities:
Purchases of available-for-sale securities	(903,240)	(217,920)	(952,995)
Proceeds from sales of available-for-sale securities	123,270	98,402	57,804
Net cash (used for) provided by investing activities	(774,642)	(1,669,670)	(1,137,123)
Financing activities:
Issuance of long-term debt	0	150,000	0
Repayment of long-term debt	0	(150,000)	(102,579)
Cash dividends paid to common shareholders	(80,964)	(67,431)	(48,952)
Cash dividends paid to preferred shareholders	(8,711)	(10,556)	(10,803)
Exercise of stock options	3,060	2,221	2,736
Excess tax benefits from stock-based compensation	2,338	1,161	389
Common stock issued	0	435	731
Common stock repurchased/shares acquired related to employee share-based plans	(12,564)	(10,741)	0
Common stock warrants repurchased	(23)	(3)	(30)
Net cash (used for) provided by financing activities	457,171	1,434,783	644,503
Net (decrease) increase in cash and due from banks	(10,286)	37,928	(28,667)
Cash and due from banks at beginning of period	261,544	223,616	252,283
Cash and due from banks at end of period	251,258	261,544	223,616
Parent Company [Member]
Operating activities:
Net income	206,340	199,726	179,456
Equity in undistributed earnings of subsidiaries and associated companies	(117,074)	(113,068)	(101,682)
Stock-based compensation	10,935	10,223	10,664
Other, net	9,066	(10,721)	(1,934)
Net cash provided by operating activities	109,267	86,160	86,504
Investing activities:
Purchases of available-for-sale securities	0	(3,500)	(75)
Proceeds from sales of available-for-sale securities	0	3,499	13,544
Net cash (used for) provided by investing activities	0	(1)	13,469
Financing activities:
Issuance of long-term debt	0	150,000	0
Repayment of long-term debt	0	(150,000)	0
Cash dividends paid to common shareholders	(80,964)	(67,431)	(48,952)
Cash dividends paid to preferred shareholders	(8,711)	(10,556)	(10,803)
Exercise of stock options	3,060	2,221	2,736
Excess tax benefits from stock-based compensation	2,338	1,161	389
Common stock issued	0	435	731
Common stock repurchased/shares acquired related to employee share-based plans	(17,815)	(13,067)	(672)
Common stock warrants repurchased	(23)	(3)	(30)
Net cash (used for) provided by financing activities	(102,115)	(87,240)	(56,601)
Net (decrease) increase in cash and due from banks	7,152	(1,081)	43,372
Cash and due from banks at beginning of period	272,492	273,573	230,201
Cash and due from banks at end of period	$ 279,644	$ 272,492	$ 273,573