Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010
Cash and cash equivalents	$ 206,167		$ 15,627	$ 17,387	$ 16,055
Accounts receivable	299,316		341,915
Inventories	37,323		46,234
Other current assets	685,601		574,502
Total current assets	1,228,407		978,278
Intercompany receivables	0		0
Property and equipment	11,643,954		11,060,819
Less: Accumulated depreciation, depletion and amortization	4,617,882		4,415,339
Property and equipment, net	7,026,072		6,645,480
Investments in subsidiaries (equity method)	0		0
Other assets	299,682		279,139
TOTAL ASSETS	8,554,161	[1]	7,902,897	6,340,748
Accounts and notes payable	576,040		576,527
Other current liabilities	384,604		308,386
Total current liabilities	960,644		884,913
Intercompany payables	0		0
Long-term debt	1,669,380		1,342,100
Deferred income taxes	1,660,284		1,586,798
Other liabilities	112,094		119,782
Total liabilities	4,402,402		3,933,593
Commitments and Contingencies
Total Equity	4,151,759		3,969,304
TOTAL LIABILITIES AND EQUITY	8,554,161		7,902,897
Parent [Member]
Cash and cash equivalents	205,415		14,711	14,743	8,381
Accounts receivable	2,940		2,914
Inventories	0		0
Other current assets	4,703		6,087
Total current assets	213,058		23,712
Intercompany receivables	2,068,919		2,053,132
Property and equipment	194,097		180,300
Less: Accumulated depreciation, depletion and amortization	61,540		57,254
Property and equipment, net	132,557		123,046
Investments in subsidiaries (equity method)	3,433,064		3,256,195
Other assets	36,212		28,641
TOTAL ASSETS	5,883,810		5,484,726
Accounts and notes payable	96,277		206,541
Other current liabilities	13,033		4,712
Total current liabilities	109,310		211,253
Intercompany payables	0		0
Long-term debt	1,669,380		1,342,100
Deferred income taxes	(96,880)		(97,045)
Other liabilities	50,241		59,114
Total liabilities	1,732,051		1,515,422
Total Equity	4,151,759		3,969,304
TOTAL LIABILITIES AND EQUITY	5,883,810		5,484,726
Guarantors [Member]
Cash and cash equivalents	489		0	1,995	7,631
Accounts receivable	260,402		309,038
Inventories	36,408		45,260
Other current assets	679,271		563,635
Total current assets	976,570		917,933
Intercompany receivables	41		53
Property and equipment	10,271,762		9,731,944
Less: Accumulated depreciation, depletion and amortization	4,405,113		4,220,205
Property and equipment, net	5,866,649		5,511,739
Investments in subsidiaries (equity method)	0		0
Other assets	240,120		227,152
TOTAL ASSETS	7,083,380		6,656,877
Accounts and notes payable	430,906		332,710
Other current liabilities	370,224		301,170
Total current liabilities	801,130		633,880
Intercompany payables	1,728,162		1,628,750
Long-term debt	0		0
Deferred income taxes	1,492,017		1,442,576
Other liabilities	56,198		54,826
Total liabilities	4,077,507		3,760,032
Total Equity	3,005,873		2,896,845
TOTAL LIABILITIES AND EQUITY	7,083,380		6,656,877
Non-Guarantors [Member]
Cash and cash equivalents	263		916	649	43
Accounts receivable	35,974		29,963
Inventories	915		974
Other current assets	1,627		4,780
Total current assets	38,779		36,633
Intercompany receivables	22,329		23,517
Property and equipment	1,178,095		1,148,575
Less: Accumulated depreciation, depletion and amortization	151,229		137,880
Property and equipment, net	1,026,866		1,010,695
Investments in subsidiaries (equity method)	0		0
Other assets	23,350		23,346
TOTAL ASSETS	1,111,324		1,094,191
Accounts and notes payable	48,857		37,276
Other current liabilities	1,347		2,504
Total current liabilities	50,204		39,780
Intercompany payables	363,127		447,952
Long-term debt	0		0
Deferred income taxes	265,147		241,267
Other liabilities	5,655		5,842
Total liabilities	684,133		734,841
Total Equity	427,191		359,350
TOTAL LIABILITIES AND EQUITY	1,111,324		1,094,191
Eliminations [Member]
Cash and cash equivalents	0		0	0	0
Accounts receivable	0		0
Inventories	0		0
Other current assets	0		0
Total current assets	0		0
Intercompany receivables	(2,091,289)		(2,076,702)
Property and equipment	0		0
Less: Accumulated depreciation, depletion and amortization	0		0
Property and equipment, net	0		0
Investments in subsidiaries (equity method)	(3,433,064)		(3,256,195)
Other assets	0		0
TOTAL ASSETS	(5,524,353)		(5,332,897)
Accounts and notes payable	0		0
Other current liabilities	0		0
Total current liabilities	0		0
Intercompany payables	(2,091,289)		(2,076,702)
Long-term debt	0		0
Deferred income taxes	0		0
Other liabilities	0		0
Total liabilities	(2,091,289)		(2,076,702)
Total Equity	(3,433,064)		(3,256,195)
TOTAL LIABILITIES AND EQUITY	$ (5,524,353)		$ (5,332,897)

[1] (2) Other assets represent corporate assets not allocated to segments and assets, including investments in cash equivalents, for non-reportable segments.