Consolidated Statements of Changes in Shareholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balance at Dec. 31, 2012	$ 2,595,909	$ 373,623	$ (1,850)	$ 1,645,958	$ 615,436	$ (37,258)
Balance, Shares at Dec. 31, 2012	186,811,642
Total comprehensive income	106,648				132,338	(25,690)
Issuance of common stock and share-based awards under employee benefit plans (shares)		679,487
Issuance of common stock and share-based awards under employee benefit plans	6,783	1,359		5,424
Treasury stock purchased	(68)		(68)
Cash dividends paid on common stock	(29,924)				(29,924)
Balance at Sep. 30, 2013	2,679,348	374,982	(1,918)	1,651,382	717,850	(62,948)
Balance, shares at Sep. 30, 2013	187,491,129
Balance at Dec. 31, 2013	2,717,587	375,353	(2,531)	1,652,116	744,215	(51,566)
Balance, Shares at Dec. 31, 2013	187,676,711
Total comprehensive income	139,559				114,124	25,435
Issuance of common stock and share-based awards under employee benefit plans (shares)		463,943
Issuance of common stock and share-based awards under employee benefit plans	7,915	929		6,986
Retirement of common stock (Shares)		(6,461,833)
Retirement of common stock	(66,355)	(12,924)		(53,431)
Treasury stock purchased	(569)		(569)
Cash dividends paid on common stock	(46,877)				(46,877)
Balance at Sep. 30, 2014	$ 2,751,260	$ 363,358	$ (3,100)	$ 1,605,671	$ 811,462	$ (26,131)
Balance, shares at Sep. 30, 2014	181,678,821