Correction of Prior Period Financial Statement (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010		Dec. 31, 2009		Dec. 31, 2008
Assets
Current deferred income taxes	$ 43,032	$ 54,704
Prepaid expenses	21,598	20,109
Total current assets	863,100	773,751
Total assets	8,229,314	8,339,536		8,526,500
Liabilities
Other accrued liabilities	95,383	129,084
Total current liabilities	406,253	582,348
Noncurrent deferred income taxes	732,528	843,599
Total liabilities	4,437,697	4,383,738
Equity
Retained earnings	1,334,476	1,503,681
Total equity	3,791,617	3,955,798	[1]	4,028,055	[1]	3,529,785	[1]
Total liabilities and equity	8,229,314	8,339,536
As Reported [Member]
Assets
Current deferred income taxes		53,794
Prepaid expenses		19,374
Total current assets		772,106
Total assets		8,337,891
Liabilities
Other accrued liabilities		112,408
Total current liabilities		565,672
Noncurrent deferred income taxes		849,448
Total liabilities		4,372,911
Equity
Retained earnings		1,512,863
Total equity		3,964,980
Total liabilities and equity		8,337,891
Correction [Member]
Assets
Current deferred income taxes		910
Prepaid expenses		735
Total current assets		1,645
Total assets		1,645
Liabilities
Other accrued liabilities		16,676
Total current liabilities		16,676
Noncurrent deferred income taxes		(5,849)
Total liabilities		10,827
Equity
Retained earnings		(9,182)
Total equity		(9,182)
Total liabilities and equity		$ 1,645

[1] As Restated, See Note 20