Consolidated Statements of Common Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Other Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2008	$ 2,746,076	$ 184,208	$ 938,299	$ 1,616,830	$ 10,365	$ (3,626)
Treasury stock (in shares) at Dec. 31, 2008						(538,921)
Balance (in shares) at Dec. 31, 2008		184,208,283
Comprehensive income:
Net income	(123,274)		0	(123,274)	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	(51,684)		0	0	(51,684)
Postretirement liability adjustment	9,918		0	0	9,918
Foreign currency translation adjustment, net of tax	10,568		0	0	10,568
Net unrealized gains on available-for-sale investments, net of tax	0
Total comprehensive income	(154,472)		0	0	0
Dividends, Preferred Stock, Cash	(685)		0	(685)	0
Dividends, Common Stock, Cash	(115,832)		0	(115,832)	0
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	(117)		(117)	0	0
Issuance of common stock (in shares)		4,180,982
Issuance of common stock	81,677	4,181	77,496
Balance at Dec. 31, 2009	2,556,647	188,389	1,015,678	1,377,039	(20,833)	(3,626)
Treasury stock (in shares) at Dec. 31, 2009						(538,921)
Balance (in shares) at Dec. 31, 2009		188,389,265
Comprehensive income:
Net income	240,659		0	240,659	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	673		0	0	673
Postretirement liability adjustment	(5,730)		0	0	(5,730)
Foreign currency translation adjustment, net of tax	(5,371)		0	0	(5,371)
Net unrealized gains on available-for-sale investments, net of tax	0
Total comprehensive income	230,231		0	0	0
Dividends, Preferred Stock, Cash	(685)		0	(685)	0
Dividends, Common Stock, Cash	(119,574)		0	(119,574)	0
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	924		924	0	0
Issuance of common stock (in shares)		512,114
Issuance of common stock	10,259	512	9,747
Balance at Dec. 31, 2010	2,677,802	188,901	1,026,349	1,497,439	(31,261)	(3,626)
Treasury stock (in shares) at Dec. 31, 2010	(538,921)					(538,921)
Balance (in shares) at Dec. 31, 2010	188,901,379	188,901,379
Comprehensive income:
Net income	213,026		0	213,026	0
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax	7,900		0	0	7,900
Postretirement liability adjustment	(22,427)		0	0	(22,427)
Foreign currency translation adjustment, net of tax	(1,295)		0	0	(1,295)
Net unrealized gains on available-for-sale investments, net of tax	82		0	0	82
Total comprehensive income	197,286		0	0	0
Dividends, Preferred Stock, Cash	(685)		0	(685)	0
Dividends, Common Stock, Cash	(123,657)		0	(123,657)	0
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation	(909)		(909)	0	0
Issuance of common stock (in shares)		431,106
Issuance of common stock	10,730	431	10,299
Balance at Dec. 31, 2011	$ 2,760,567	$ 189,332	$ 1,035,739	$ 1,586,123	$ (47,001)	$ (3,626)
Treasury stock (in shares) at Dec. 31, 2011	(538,921)					(538,921)
Balance (in shares) at Dec. 31, 2011	189,332,485	189,332,485