Condensed Consolidating Financial Information (Condensed Consolidating Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012	Sep. 30, 2012		Dec. 31, 2011
Cash and cash equivalents	$ 18,950		$ 53,583	$ 18,560		$ 15,627
Restricted cash			8,542
Accounts receivable	444,723		377,638
Inventories	43,225		28,141
Other current assets	233,077		341,008
Total current assets	739,975		808,912
Property and equipment	14,823,553		13,028,439
Less: Accumulated depreciation, depletion and amortization	(7,786,820)		(7,191,463)
Total property and equipment, net	7,036,733		5,836,976
Other assets	117,680		91,639
TOTAL ASSETS	7,894,388	[1]	6,737,527	7,356,562	[1],[2]
Accounts payable	663,726		556,980
Other current liabilities	146,085		210,791
Total current liabilities	809,811		767,771
Long-term debt	1,911,165		1,668,273
Deferred income taxes	1,388,833		1,049,138
Other liabilities	264,590		216,473
Total liabilities	4,374,399		3,701,655
Commitments and Contingencies
Total Equity	3,519,989		3,035,872
TOTAL LIABILITIES AND EQUITY	7,894,388		6,737,527
Parent [Member]
Cash and cash equivalents	17,956		47,491	16,961		14,711
Restricted cash			8,542
Accounts receivable	3,114		2,677
Inventories			2
Other current assets	13,893		7,461
Total current assets	34,963		66,173
Intercompany receivables	2,548,900		2,259,713
Property and equipment	236,324		220,837
Less: Accumulated depreciation, depletion and amortization	(102,706)		(82,178)
Total property and equipment, net	133,618		138,659
Investments in subsidiaries (equity method)	2,788,544		2,309,947
Other assets	32,103		35,136
TOTAL ASSETS	5,538,128		4,809,628
Accounts payable	147,265		140,367
Other current liabilities	3,759		3,758
Total current liabilities	151,024		144,125
Long-term debt	1,911,165		1,668,273
Deferred income taxes	(115,675)		(116,207)
Other liabilities	71,625		77,565
Total liabilities	2,018,139		1,773,756
Total Equity	3,519,989		3,035,872
TOTAL LIABILITIES AND EQUITY	5,538,128		4,809,628
Guarantors [Member]
Cash and cash equivalents			5,988	1,365
Accounts receivable	423,418		353,607
Inventories	40,906		26,975
Other current assets	212,154		321,396
Total current assets	676,478		707,966
Intercompany receivables	57		42
Property and equipment	13,079,991		11,491,222
Less: Accumulated depreciation, depletion and amortization	(7,455,008)		(6,923,106)
Total property and equipment, net	5,624,983		4,568,116
Other assets	69,697		42,247
TOTAL ASSETS	6,371,215		5,318,371
Accounts payable	432,089		375,604
Other current liabilities	141,307		205,623
Total current liabilities	573,396		581,227
Intercompany payables	2,603,488		2,108,360
Deferred income taxes	1,077,055		820,279
Other liabilities	178,703		124,505
Total liabilities	4,432,642		3,634,371
Total Equity	1,938,573		1,684,000
TOTAL LIABILITIES AND EQUITY	6,371,215		5,318,371
Non-Guarantors [Member]
Cash and cash equivalents	994		104	234		916
Accounts receivable	18,191		21,354
Inventories	2,319		1,164
Other current assets	7,030		12,151
Total current assets	28,534		34,773
Intercompany receivables	54,531		27,077
Property and equipment	1,507,238		1,316,380
Less: Accumulated depreciation, depletion and amortization	(229,106)		(186,179)
Total property and equipment, net	1,278,132		1,130,201
Other assets	15,880		14,256
TOTAL ASSETS	1,377,077		1,206,307
Accounts payable	84,372		41,009
Other current liabilities	1,019		1,410
Total current liabilities	85,391		42,419
Intercompany payables			178,472
Deferred income taxes	427,453		345,066
Other liabilities	14,262		14,403
Total liabilities	527,106		580,360
Total Equity	849,971		625,947
TOTAL LIABILITIES AND EQUITY	1,377,077		1,206,307
Eliminations [Member]
Intercompany receivables	(2,603,488)		(2,286,832)
Investments in subsidiaries (equity method)	(2,788,544)		(2,309,947)
TOTAL ASSETS	(5,392,032)		(4,596,779)
Intercompany payables	(2,603,488)		(2,286,832)
Total liabilities	(2,603,488)		(2,286,832)
Total Equity	(2,788,544)		(2,309,947)
TOTAL LIABILITIES AND EQUITY	$ (5,392,032)		$ (4,596,779)

[1] Interest expense and the provision for income taxes by segment are allocated as they are incurred at the corporate level.

[2] Capital investments includes decreases of $14.6 million and $56.2 million for the three-month periods ended September 30, 2013 and 2012, respectively, and increase of $25.8 million and decrease of $40.7 million for the nine-month periods ended September 30, 2013 and 2012, respectively, relating to the change in accrued expenditures between periods.