Parent Company Information (Components of Condensed Cash Flow The Parent Company) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation	$ 11,438	$ 10,935	$ 10,223
Gain on redemption of other assets	(7,331)	0	0
Net cash provided by operating activities	398,145	302,792	242,995
Investing activities:
Purchases of available-for-sale securities	(980,870)	(903,240)	(217,920)
Proceeds from sales of available-for-sale securities	259,283	123,270	98,402
Purchases of intercompany debt securities	(381)	458	(115)
Net cash used for investing activities	(1,635,006)	(774,184)	(1,669,785)
Financing activities:
Issuance of long-term debt	0	0	150,000
Repayment of long-term debt	0	0	(150,000)
Cash dividends paid to common shareholders	(89,522)	(80,964)	(67,431)
Cash dividends paid to preferred shareholders	(8,096)	(8,711)	(10,556)
Exercise of stock options	11,762	3,060	2,221
Excess tax benefits from stock-based compensation	3,204	2,338	1,161
Common stock issued	0	0	435
Common stock repurchased/shares acquired related to employee share-based plans	(11,206)	(12,564)	(10,741)
Common stock warrants repurchased	(163)	(23)	(3)
Net cash (used for) provided by financing activities	1,227,831	457,171	1,434,783
Net (decrease) increase in cash and due from banks	(9,030)	(14,221)	7,993
Cash and due from banks at beginning of period	199,693	213,914	205,921
Cash and due from banks at end of period	190,663	199,693	213,914
Parent Company [Member]
Operating activities:
Net income	207,127	204,729	199,726
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of subsidiaries and associated companies	(79,599)	(115,463)	(113,068)
Stock-based compensation	11,438	10,935	10,223
Gain on redemption of other assets	(7,331)	0	0
Other, net	(3,736)	9,066	(10,721)
Net cash provided by operating activities	127,899	109,267	86,160
Investing activities:
Purchases of available-for-sale securities	0	0	(3,500)
Proceeds from sales of available-for-sale securities	1,089	0	3,499
Purchases of intercompany debt securities	(150,000)	0	0
Net cash used for investing activities	(148,911)	0	(1)
Financing activities:
Issuance of long-term debt	0	0	150,000
Repayment of long-term debt	0	0	(150,000)
Cash dividends paid to common shareholders	(89,522)	(80,964)	(67,431)
Cash dividends paid to preferred shareholders	(8,096)	(8,711)	(10,556)
Exercise of stock options	11,762	3,060	2,221
Excess tax benefits from stock-based compensation	3,204	2,338	1,161
Common stock issued	0	0	435
Common stock repurchased/shares acquired related to employee share-based plans	(22,870)	(17,815)	(13,067)
Common stock warrants repurchased	(163)	(23)	(3)
Net cash (used for) provided by financing activities	(105,685)	(102,115)	(87,240)
Net (decrease) increase in cash and due from banks	(126,697)	7,152	(1,081)
Cash and due from banks at beginning of period	279,644	272,492	273,573
Cash and due from banks at end of period	$ 152,947	$ 279,644	$ 272,492