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	59,383				88,047	(28,664)
Issuance of common stock and share-based awards under employee benefit plans (shares)		471,555
Issuance of common stock and share-based awards under employee benefit plans	4,621	943		3,678
Treasury stock purchased	(25)		(25)
Cash dividends paid on common stock	(14,948)				(14,948)
Balance at Jun. 30, 2013	2,644,940	374,566	(1,875)	1,649,636	688,535	(65,922)
Balance, shares at Jun. 30, 2013	187,283,197
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	102,980				80,656	22,324
Issuance of common stock and share-based awards under employee benefit plans (shares)		396,235
Issuance of common stock and share-based awards under employee benefit plans	6,376	793		5,583
Treasury stock purchased	(544)		(544)
Cash dividends paid on common stock	(30,007)				(30,007)
Balance at Jun. 30, 2014	$ 2,796,392	$ 376,146	$ (3,075)	$ 1,657,699	$ 794,864	$ (29,242)
Balance, shares at Jun. 30, 2014	188,072,946