Parent Company Information (Components of Condensed Cash Flow The Parent Company) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Operating activities:
Stock-based compensation	$ 10,223		$ 10,664		$ 8,955
Net cash provided by operating activities	272,815		476,724		257,082
Investing activities:
Increase in interest-bearing deposits	(109,021)		31,761		(2,143)
Purchases of available for sale securities	(217,920)		(952,995)		(1,204,079)
Proceeds from maturities and principal payments of available for sale securities	416,821		741,467		854,747
Proceeds from sales of available-for-sale securities	98,402	[1]	57,804	[1]	148,222	[1]
Net cash used for investing activities	(1,669,644)		(1,149,932)		(1,390,229)
Financing activities:
Issuance of long-term debt	150,000		0		0
Repayment of long-term debt	(150,000)		(102,579)		(210,971)
Preferred stock issued	0		0		122,710
Cash dividends paid to common shareholders	(67,431)		(48,952)		(30,667)
Cash dividends paid to preferred shareholders	(10,556)		(10,803)		(2,460)
Exercise of stock options	2,221		2,736		996
Excess tax benefits from stock-based compensation	1,161		389		812
Common stock issued	435		731		560
Common stock repurchased	(10,741)		0		(50,000)
Common stock warrants repurchased	(3)		(30)		(388)
Net cash used for financing activities	1,434,757		644,541		1,189,473
Net increase (decrease) in cash and due from banks	37,928		(28,667)		56,326
Cash and due from banks at beginning of period	223,616		252,283		195,957
Cash and due from banks at end of period	261,544		223,616		252,283
Parent Company [Member]
Operating activities:
Net income	199,752		179,549		173,697
Equity in undistributed earnings of subsidiaries and associated companies	(113,094)		(101,775)		(52,287)
Stock-based compensation	10,223		10,664		8,955
Other, net	(10,721)		(1,934)		(7,422)
Net cash provided by operating activities	86,160		86,504		122,943
Investing activities:
Increase in interest-bearing deposits	(14)		(41,011)		(24,081)
Purchases of available for sale securities	(3,500)		(75)		(8,272)
Proceeds from maturities and principal payments of available for sale securities	0		0		775
Proceeds from sales of available-for-sale securities	3,499		13,544		1,073
Net cash used for investing activities	(15)		(27,542)		(30,505)
Financing activities:
Issuance of long-term debt	150,000		0		0
Repayment of long-term debt	(150,000)		0		(136,070)
Preferred stock issued	0		0		122,710
Cash dividends paid to common shareholders	(67,431)		(48,952)		(30,667)
Cash dividends paid to preferred shareholders	(10,556)		(10,803)		(2,460)
Exercise of stock options	2,221		2,736		996
Excess tax benefits from stock-based compensation	1,161		389		812
Common stock issued	435		731		560
Common stock repurchased	(13,067)		(672)		(53,243)
Common stock warrants repurchased	(3)		(30)		(388)
Net cash used for financing activities	(87,240)		(56,601)		(97,750)
Net increase (decrease) in cash and due from banks	(1,095)		2,361		(5,312)
Cash and due from banks at beginning of period	12,452		10,091		15,403
Cash and due from banks at end of period	$ 11,357		$ 12,452		$ 10,091

[1] Proceeds from sales, for the year ended December 31, 2014, do not include $28.2 million of unsettled sales transactions at December 31, 2014. The gross realized gains and gross realized losses for the year ended December 31, 2014 reflect the unsettled sales transactions.