Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash and cash equivalents	$ 22,938	$ 53,583	$ 15,627	$ 16,055
Restricted cash		8,542
Accounts receivable	464,045	377,638
Inventories	37,745	28,141
Other current assets		341,008
Total current assets	644,175	808,912
Property and equipment		13,028,439
Less: Accumulated depreciation, depletion and amortization	(8,005,836)	(7,191,463)
Total property and equipment, net	7,296,623	5,836,976
Other assets	106,928	91,639
TOTAL ASSETS	8,047,726	6,737,527	7,902,897
Accounts payable		556,980
Other current liabilities		210,791
Total current liabilities	688,011	767,771
Long-term debt	1,950,096	1,668,273
Deferred income taxes	1,532,329	1,049,138
Other liabilities		216,473
Total liabilities		3,701,655
Total Equity	3,622,030	3,035,872	3,969,304	2,964,876
TOTAL LIABILITIES AND EQUITY	8,047,726	6,737,527
Parent [Member]
Cash and cash equivalents		47,491	14,711	8,381
Accounts receivable		2,677
Inventories		2
Other current assets		7,461
Total current assets		66,173
Intercompany receivables		2,259,713
Property and equipment		220,837
Less: Accumulated depreciation, depletion and amortization		(82,178)
Total property and equipment, net		138,659
Investments in subsidiaries (equity method)		2,309,947
Other assets		35,136
TOTAL ASSETS		4,809,628
Accounts payable		140,367
Other current liabilities		3,758
Total current liabilities		144,125
Long-term debt		1,668,273
Deferred income taxes		(116,207)
Other liabilities		77,565
Total liabilities		1,773,756
Total Equity		3,035,872
TOTAL LIABILITIES AND EQUITY		4,809,628
Guarantors [Member]
Cash and cash equivalents		5,988		7,631
Accounts receivable		353,607
Inventories		26,975
Other current assets		321,396
Total current assets		707,966
Intercompany receivables		42
Property and equipment		11,491,222
Less: Accumulated depreciation, depletion and amortization		(6,923,106)
Total property and equipment, net		4,568,116
Other assets		42,247
TOTAL ASSETS		5,318,371
Accounts payable		375,604
Other current liabilities		205,623
Total current liabilities		581,227
Intercompany payables		2,108,360
Deferred income taxes		820,279
Other liabilities		124,505
Total liabilities		3,634,371
Total Equity		1,684,000
TOTAL LIABILITIES AND EQUITY		5,318,371
Non-Guarantors [Member]
Cash and cash equivalents		104	916	43
Accounts receivable		21,354
Inventories		1,164
Other current assets		12,151
Total current assets		34,773
Intercompany receivables		27,077
Property and equipment		1,316,380
Less: Accumulated depreciation, depletion and amortization		(186,179)
Total property and equipment, net		1,130,201
Other assets		14,256
TOTAL ASSETS		1,206,307
Accounts payable		41,009
Other current liabilities		1,410
Total current liabilities		42,419
Intercompany payables		178,472
Deferred income taxes		345,066
Other liabilities		14,403
Total liabilities		580,360
Total Equity		625,947
TOTAL LIABILITIES AND EQUITY		1,206,307
Eliminations [Member]
Intercompany receivables		(2,286,832)
Investments in subsidiaries (equity method)		(2,309,947)
TOTAL ASSETS		(4,596,779)
Intercompany payables		(2,286,832)
Total liabilities		(2,286,832)
Total Equity		(2,309,947)
TOTAL LIABILITIES AND EQUITY		$ (4,596,779)