Consolidated Statements of Stockholders' Equity (USD $) In Thousands, except Share data	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Gains (Losses) [Member]	Treasury Stock [Member]
Beginning Balance at Dec. 31, 2010	$ 3,861,712	$ 1,439	$ 1,972,550	$ 1,998,995	$ 3,141	$ (114,413)
Beginning Balance, shares at Dec. 31, 2010		143,943,624				4,916,800
Net income	962,542			962,542
Dividends to stockholders ($3.50 per share)	(486,595)			(486,595)
Anti-dilution adjustment paid to stock plan participants ($3.00 per share)	(2,632)			(2,632)
Stock options exercised, shares		385
Stock-based compensation, net of tax	5,819		5,819
Net gain (loss) on derivative financial instruments	(7,353)				(7,353)
Net gain (loss) on investments	(430)				(430)
Ending Balance at Dec. 31, 2011	4,333,063	1,439	1,978,369	2,472,310	(4,642)	(114,413)
Ending Balance, Shares at Dec. 31, 2011		143,944,009				4,916,800
Net income	720,477			720,477
Dividends to stockholders ($3.50 per share)	(486,603)			(486,603)
Anti-dilution adjustment paid to stock plan participants ($3.00 per share)	(3,269)			(3,269)
Stock options exercised	148		148
Stock options exercised, shares		4,361
Stock-based compensation, net of tax	5,440		5,440
Net gain (loss) on derivative financial instruments	6,970				6,970
Net gain (loss) on investments	168				168
Ending Balance at Dec. 31, 2012	4,576,394	1,439	1,983,957	2,702,915	2,496	(114,413)
Ending Balance, Shares at Dec. 31, 2012		143,948,370				4,916,800
Net income	548,686			548,686
Dividends to stockholders ($3.50 per share)	(486,620)			(486,620)
Anti-dilution adjustment paid to stock plan participants ($3.00 per share)	(3,820)			(3,820)
Stock options exercised	110	1	109
Stock options exercised, shares	15,091	3,878
Stock-based compensation, net of tax	4,654		4,654
Net gain (loss) on derivative financial instruments	(1,993)				(1,993)
Net gain (loss) on investments	(153)				(153)
Ending Balance at Dec. 31, 2013	$ 4,637,258	$ 1,440	$ 1,988,720	$ 2,761,161	$ 350	$ (114,413)
Ending Balance, Shares at Dec. 31, 2013		143,952,248				4,916,800