CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Details 2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 680	$ 3,012	$ 474,139	$ 217,569
Accounts receivable	60,012	79,089
Other current assets	188,382	128,571
Total current assets	249,074	210,672
Property and equipment, at cost	10,051,251	9,601,102
Less accumulated depreciation, depletion, and amortization	7,472,922	6,949,986
Net property and equipment	2,578,329	2,651,116
Investment in subsidiaries	0	0
Goodwill	239,420	239,420
Due from subsidiaries	0	0
Deferred income taxes	0	231,116
Other assets	50,507	48,827
TOTAL ASSETS	3,117,330	3,381,151
Current liabilities:
Accounts payable and accrued liabilities	212,284	247,880
Other current liabilities	109,799	92,957
Total current liabilities	322,083	340,837
Long-term debt	1,938,906	1,693,044
Due to parent and subsidiaries	0	0
Deferred income taxes	0	0
Other liabilities	160,216	154,157
Total liabilities	2,421,205	2,188,038
Shareholders' equity	696,125	1,193,113
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	3,117,330	3,381,151
Parent Company
Current assets:
Cash and cash equivalents	576	1,734
Accounts receivable	32,477	43,999
Other current assets	187,423	127,667
Total current assets	220,476	173,400
Property and equipment, at cost	8,433,261	8,000,466
Less accumulated depreciation, depletion, and amortization	6,230,964	5,782,409
Net property and equipment	2,202,297	2,218,057
Investment in subsidiaries	142,587	160,591
Goodwill	216,460	216,460
Due from subsidiaries	156,249	214,394
Deferred income taxes	98,931	312,564
Other assets	50,507	48,827
TOTAL ASSETS	3,087,507	3,344,293
Current liabilities:
Accounts payable and accrued liabilities	205,110	235,788
Other current liabilities	103,395	86,618
Total current liabilities	308,505	322,406
Long-term debt	1,938,906	1,693,044
Due to parent and subsidiaries	0	0
Deferred income taxes	0	0
Other liabilities	143,971	135,730
Total liabilities	2,391,382	2,151,180
Shareholders' equity	696,125	1,193,113
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	3,087,507	3,344,293
Guarantor Subsidiary
Current assets:
Cash and cash equivalents	2	1	0	3
Accounts receivable	26,501	34,142
Other current assets	314	313
Total current assets	26,817	34,456
Property and equipment, at cost	1,395,315	1,317,917
Less accumulated depreciation, depletion, and amortization	1,140,022	1,102,339
Net property and equipment	255,293	215,578
Investment in subsidiaries	0	0
Goodwill	22,960	22,960
Due from subsidiaries	46,702	46,944
Deferred income taxes	0	0
Other assets	0	0
TOTAL ASSETS	351,772	319,938
Current liabilities:
Accounts payable and accrued liabilities	3,025	8,846
Other current liabilities	90	63
Total current liabilities	3,115	8,909
Long-term debt	0	0
Due to parent and subsidiaries	0	0
Deferred income taxes	126,929	107,012
Other liabilities	3,504	2,614
Total liabilities	133,548	118,535
Shareholders' equity	218,224	201,403
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	351,772	319,938
Combined Non-Guarantor Subsidiaries
Current assets:
Cash and cash equivalents	102	1,277	833	986
Accounts receivable	2,299	2,201
Other current assets	645	591
Total current assets	3,046	4,069
Property and equipment, at cost	222,675	282,719
Less accumulated depreciation, depletion, and amortization	101,936	65,238
Net property and equipment	120,739	217,481
Investment in subsidiaries	0	0
Goodwill	0	0
Due from subsidiaries	0	0
Deferred income taxes	27,998	25,564
Other assets	0	0
TOTAL ASSETS	151,783	247,114
Current liabilities:
Accounts payable and accrued liabilities	5,414	4,499
Other current liabilities	6,314	6,276
Total current liabilities	11,728	10,775
Long-term debt	0	0
Due to parent and subsidiaries	202,951	261,338
Deferred income taxes	0	0
Other liabilities	12,741	15,813
Total liabilities	227,420	287,926
Shareholders' equity	(75,637)	(40,812)
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	151,783	247,114
Eliminations
Current assets:
Cash and cash equivalents	0	0
Accounts receivable	(1,265)	(1,253)
Other current assets	0	0
Total current assets	(1,265)	(1,253)
Property and equipment, at cost	0	0
Less accumulated depreciation, depletion, and amortization	0	0
Net property and equipment	0	0
Investment in subsidiaries	(142,587)	(160,591)
Goodwill	0	0
Due from subsidiaries	(202,951)	(261,338)
Deferred income taxes	(126,929)	(107,012)
Other assets	0	0
TOTAL ASSETS	(473,732)	(530,194)
Current liabilities:
Accounts payable and accrued liabilities	(1,265)	(1,253)
Other current liabilities	0	0
Total current liabilities	(1,265)	(1,253)
Long-term debt	0	0
Due to parent and subsidiaries	(202,951)	(261,338)
Deferred income taxes	(126,929)	(107,012)
Other liabilities	0	0
Total liabilities	(331,145)	(369,603)
Shareholders' equity	(142,587)	(160,591)
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ (473,732)	$ (530,194)