Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Statement Of Stockholders Equity [Abstract]
Total shareholders' equity at beginning of period	$ 2,417,482	$ 2,283,537
Net income	114,851	119,095
Other comprehensive income (loss)	(82,446)	5,541
Stock option exercises (662,224 shares in 2013 and 140,311 shares in 2012)	34,189	7,211
Stock compensation expense recognized in earnings	4,985	5,398
Tax benefits (deficiencies) related to stock compensation	(73)	(414)
Issuance of preferred stock (6,000,000 shares in 2013)	144,486
Purchase of treasury stock (1,905,077 shares in 2013)	(115,200)
Accelerated share repurchase forward contract	(28,800)
Cash dividends - preferred stock (approximately $0.45 per share in 2013)	(2,688)
Cash dividends - common stock ($0.98 per share in 2013 and $0.94 per share in 2012)	(58,948)	(57,757)
Total shareholders' equity at end of period	$ 2,427,838	$ 2,362,611