Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash and cash equivalents	$ 53,583	$ 15,627	$ 16,055	$ 13,184
Restricted cash	8,542
Accounts receivable	377,638	341,915
Inventories	28,141	46,234
Other current assets	341,008	574,502
Total current assets	808,912	978,278
Property and equipment	13,028,439	11,060,819
Less: Accumulated depreciation, depletion and amortization	(7,191,463)	(4,415,339)
Total property and equipment, net	5,836,976	6,645,480
Other assets	91,639	279,139
TOTAL ASSETS	6,737,527	7,902,897	6,017,463
Accounts payable	556,980	575,327
Other current liabilities	210,791	309,586
Total current liabilities	767,771	884,913
Long-term debt	1,668,273	1,342,100
Deferred income taxes	1,049,138	1,586,798
Other liabilities	216,473	119,782
Total liabilities	3,701,655	3,933,593
Total Equity	3,035,872	3,969,304	2,964,876	2,340,981
TOTAL LIABILITIES AND EQUITY	6,737,527	7,902,897
Parent [Member]
Cash and cash equivalents	47,491	14,711	8,381	7,378
Restricted cash	8,542
Accounts receivable	2,677	2,914
Inventories	2
Other current assets	7,461	6,087
Total current assets	66,173	23,712
Intercompany receivables	2,259,713	2,053,132
Property and equipment	220,837	180,300
Less: Accumulated depreciation, depletion and amortization	(82,178)	(57,254)
Total property and equipment, net	138,659	123,046
Investments in subsidiaries (equity method)	2,309,947	3,256,195
Other assets	35,136	28,641
TOTAL ASSETS	4,809,628	5,484,726
Accounts payable	140,367	205,341
Other current liabilities	3,758	5,912
Total current liabilities	144,125	211,253
Long-term debt	1,668,273	1,342,100
Deferred income taxes	(116,207)	(97,045)
Other liabilities	77,565	59,114
Total liabilities	1,773,756	1,515,422
Total Equity	3,035,872	3,969,304
TOTAL LIABILITIES AND EQUITY	4,809,628	5,484,726
Guarantors [Member]
Cash and cash equivalents	5,988		7,631	5,776
Accounts receivable	353,607	309,038
Inventories	26,975	45,260
Other current assets	321,396	563,635
Total current assets	707,966	917,933
Intercompany receivables	42	53
Property and equipment	11,491,222	9,731,944
Less: Accumulated depreciation, depletion and amortization	(6,923,106)	(4,220,205)
Total property and equipment, net	4,568,116	5,511,739
Other assets	42,247	227,152
TOTAL ASSETS	5,318,371	6,656,877
Accounts payable	375,604	332,710
Other current liabilities	205,623	301,170
Total current liabilities	581,227	633,880
Intercompany payables	2,108,360	1,628,750
Deferred income taxes	820,279	1,442,576
Other liabilities	124,505	54,826
Total liabilities	3,634,371	3,760,032
Total Equity	1,684,000	2,896,845
TOTAL LIABILITIES AND EQUITY	5,318,371	6,656,877
Non-Guarantors [Member]
Cash and cash equivalents	104	916	43	30
Accounts receivable	21,354	29,963
Inventories	1,164	974
Other current assets	12,151	4,780
Total current assets	34,773	36,633
Intercompany receivables	27,077	23,517
Property and equipment	1,316,380	1,148,575
Less: Accumulated depreciation, depletion and amortization	(186,179)	(137,880)
Total property and equipment, net	1,130,201	1,010,695
Other assets	14,256	23,346
TOTAL ASSETS	1,206,307	1,094,191
Accounts payable	41,009	37,276
Other current liabilities	1,410	2,504
Total current liabilities	42,419	39,780
Intercompany payables	178,472	447,952
Deferred income taxes	345,066	241,267
Other liabilities	14,403	5,842
Total liabilities	580,360	734,841
Total Equity	625,947	359,350
TOTAL LIABILITIES AND EQUITY	1,206,307	1,094,191
Eliminations [Member]
Intercompany receivables	(2,286,832)	(2,076,702)
Investments in subsidiaries (equity method)	(2,309,947)	(3,256,195)
TOTAL ASSETS	(4,596,779)	(5,332,897)
Intercompany payables	(2,286,832)	(2,076,702)
Total liabilities	(2,286,832)	(2,076,702)
Total Equity	(2,309,947)	(3,256,195)
TOTAL LIABILITIES AND EQUITY	$ (4,596,779)	$ (5,332,897)