Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011	Jun. 30, 2011		Dec. 31, 2010
Cash and cash equivalents	$ 41,499		$ 15,627	$ 13,279		$ 16,055
Restricted cash	144,384
Accounts receivable	272,750		341,915
Inventories	34,529		46,234
Other current assets	510,351		574,502
Total current assets	1,003,513		978,278
Property and equipment	12,053,382		11,060,819
Less: Accumulated depreciation, depletion and amortization	(5,763,882)		(4,415,339)
Total property and equipment, net	6,289,500		6,645,480
Other assets	210,950		279,139
TOTAL ASSETS	7,503,963	[1]	7,902,897	6,742,101	[1]
Accounts and notes payable	580,034		576,527
Other current liabilities	305,915		308,386
Total current liabilities	885,949		884,913
Long-term debt	1,668,811		1,342,100
Deferred income taxes	1,321,980		1,586,798
Other liabilities	111,346		119,782
Total liabilities	3,988,086		3,933,593
Total Equity	3,515,877		3,969,304
TOTAL LIABILITIES AND EQUITY	7,503,963		7,902,897
Parent [Member]
Cash and cash equivalents	36,888		14,711	13,180		8,381
Restricted cash	144,384
Accounts receivable	2,322		2,914
Other current assets	6,040		6,087
Total current assets	189,634		23,712
Intercompany receivables	2,114,806		2,053,132
Property and equipment	203,486		180,300
Less: Accumulated depreciation, depletion and amortization	(67,749)		(57,254)
Total property and equipment, net	135,737		123,046
Investments in subsidiaries (equity method)	2,794,486		3,256,195
Other assets	35,537		28,641
TOTAL ASSETS	5,270,200		5,484,726
Accounts and notes payable	109,858		206,541
Other current liabilities	9,816		4,712
Total current liabilities	119,674		211,253
Intercompany payables	10,498
Long-term debt	1,668,811		1,342,100
Deferred income taxes	(96,715)		(97,045)
Other liabilities	52,055		59,114
Total liabilities	1,754,323		1,515,422
Total Equity	3,515,877		3,969,304
TOTAL LIABILITIES AND EQUITY	5,270,200		5,484,726
Guarantors [Member]
Cash and cash equivalents	4,209					7,631
Restricted cash
Accounts receivable	246,742		309,038
Inventories	33,562		45,260
Other current assets	499,095		563,635
Total current assets	783,608		917,933
Intercompany receivables	40		53
Property and equipment	10,625,280		9,731,944
Less: Accumulated depreciation, depletion and amortization	(5,535,735)		(4,220,205)
Total property and equipment, net	5,089,545		5,511,739
Other assets	157,864		227,152
TOTAL ASSETS	6,031,057		6,656,877
Accounts and notes payable	423,901		332,710
Other current liabilities	293,916		301,170
Total current liabilities	717,817		633,880
Intercompany payables	1,832,910		1,628,750
Deferred income taxes	1,128,431		1,442,576
Other liabilities	53,112		54,826
Total liabilities	3,732,270		3,760,032
Total Equity	2,298,787		2,896,845
TOTAL LIABILITIES AND EQUITY	6,031,057		6,656,877
Non-Guarantors [Member]
Cash and cash equivalents	402		916	99		43
Restricted cash
Accounts receivable	23,686		29,963
Inventories	967		974
Other current assets	5,216		4,780
Total current assets	30,271		36,633
Intercompany receivables	24,265		23,517
Property and equipment	1,224,616		1,148,575
Less: Accumulated depreciation, depletion and amortization	(160,398)		(137,880)
Total property and equipment, net	1,064,218		1,010,695
Other assets	17,549		23,346
TOTAL ASSETS	1,136,303		1,094,191
Accounts and notes payable	46,275		37,276
Other current liabilities	2,183		2,504
Total current liabilities	48,458		39,780
Intercompany payables	295,703		447,952
Deferred income taxes	290,264		241,267
Other liabilities	6,179		5,842
Total liabilities	640,604		734,841
Total Equity	495,699		359,350
TOTAL LIABILITIES AND EQUITY	1,136,303		1,094,191
Eliminations [Member]
Restricted cash
Intercompany receivables	(2,139,111)		(2,076,702)
Investments in subsidiaries (equity method)	(2,794,486)		(3,256,195)
TOTAL ASSETS	(4,933,597)		(5,332,897)
Intercompany payables	(2,139,111)		(2,076,702)
Total liabilities	(2,139,111)		(2,076,702)
Total Equity	(2,794,486)		(3,256,195)
TOTAL LIABILITIES AND EQUITY	$ (4,933,597)		$ (5,332,897)

[1] Capital investments include an increase of $0.2 million and a reduction of $56.4 million for the three-month periods ended June 30, 2012 and 2011, respectively, and increases of $15.5 million and $57.9 million for the six-month periods ended June 30, 2012 and 2011, respectively, relating to the change in accrued expenditures between periods.