DEBT (Details) (USD $)	9 Months Ended
	Sep. 30, 2011		Jun. 30, 2011	Dec. 31, 2010
Debt
Interest rate (as a percent)	7.75%
Total debt
Debt, Principal	$ 1,885,012,000			$ 1,885,012,000
Debt, Unamortized Premium (Discount)	(13,098,000)			(16,440,000)
Debt, Other	174,000	[1]		800,000	[1]
Total debt	1,872,088,000			1,869,372,000
Less: current portion of debt
Less: current portion of debt, Principal	(285,000,000)	[2]		(285,000,000)	[2]
Less: current portion of debt, Unamortized Premium (Discount)	(323,000)	[2]		(1,292,000)	[2]
Less: current portion of debt, Other	(174,000)	[1],[2]		(800,000)	[1],[2]
Current portion of debt	(285,497,000)	[2]		(287,092,000)	[2]
Long-term portion of debt
Long-term portion of debt, Principal	1,600,012,000			1,600,012,000
Long-term portion of debt, Unamortized Premium (Discount)	(13,421,000)			(17,732,000)
Long-term portion of debt, Other	0	[1]		0	[1]
Long-term portion of debt	1,586,591,000			1,582,280,000
U.S. Credit Facility
Total debt
Debt, Principal	0			0
Debt, Unamortized Premium (Discount)	0			0
Debt, Other	0	[1]		0	[1]
Total debt	0			0
Long-term portion of debt
Revolving credit agreements	1,500,000,000		1,500,000,000
Increase in the credit agreement's borrowing capacity available subject to the agreement			300,000,000
Maximum borrowing capacity optional expansion			1,800,000,000
Borrowing base under the Credit Facilities	1,250,000,000
Reduction in borrowing base due to issue of new senior notes (as a percent)	25.00%
Fair market value of assets included in borrowing base and are sold in excess of borrowing base in effect (as a percent)	10.00%
Line of credit facility, collateral as percentage of present value of oil and gas properties (as a percent)	75.00%
Number of interest rate alternatives	2
Outstanding letters of credit	2,100,000
Minimum ratio of total debt outstanding to consolidated EBITDA, numerator	4.50
Minimum ratio of total debt outstanding to consolidated EBITDA, denominator	1.00
U.S. Credit Facility | Base rate | JPMorgan Chase Bank
Long-term portion of debt
Spread on variable rate, low end of range (as a percent)	0.50%
Spread on variable rate, high end of range (as a percent)	1.50%
U.S. Credit Facility | Federal funds rate
Long-term portion of debt
Spread on variable rate, low end of range (as a percent)	0.50%
Spread on variable rate, high end of range (as a percent)	1.50%
Spread on variable rate (as a percent)	0.50%
U.S. Credit Facility | One-month adjusted LIBO rate for one, two, three or six months
Long-term portion of debt
Spread on variable rate, low end of range (as a percent)	0.50%
Spread on variable rate, high end of range (as a percent)	1.50%
Spread on variable rate (as a percent)	1.00%
U.S. Credit Facility | Adjusted LIBO
Long-term portion of debt
Spread on variable rate, low end of range (as a percent)	1.50%
Spread on variable rate, high end of range (as a percent)	2.50%
U.S. Credit Facility | JPMorgan Chase Bank and other eleven banks
Long-term portion of debt
Commitment held by lenders (as a percent)	68.00%
Number of lenders	12
U.S. Credit Facility | Other eleven banks
Long-term portion of debt
Number of lenders	11
U.S. Credit Facility | Other lenders
Long-term portion of debt
Commitment held by lenders (as a percent)	32.00%
Commitment held by lenders, maximum (as a percent)	3.30%
8% Senior Notes due 2011
Debt
Interest rate (as a percent)	8.00%			8.00%
Total debt
Debt, Principal	285,000,000	[2]		285,000,000	[2]
Debt, Unamortized Premium (Discount)	323,000	[2]		1,292,000	[2]
Debt, Other	174,000	[1],[2]		800,000	[1],[2]
Total debt	285,497,000	[2]		287,092,000	[2]
7% Senior Subordinated Notes due 2013
Debt
Interest rate (as a percent)	7.00%			7.00%
Total debt
Debt, Principal	12,000			12,000
Debt, Unamortized Premium (Discount)	0			0
Debt, Other	0			0
Total debt	12,000			12,000
8 1/2% Senior Notes due 2014
Debt
Interest rate (as a percent)	8.50%			8.50%
Total debt
Debt, Principal	600,000,000			600,000,000
Debt, Unamortized Premium (Discount)	(13,856,000)			(18,210,000)
Debt, Other	0			0
Total debt	586,144,000			581,790,000
7 1/4% Senior Notes due 2019
Debt
Interest rate (as a percent)	7.25%			7.25%
Total debt
Debt, Principal	1,000,000,000			1,000,000,000
Debt, Unamortized Premium (Discount)	435,000			478,000
Debt, Other	0			0
Total debt	$ 1,000,435,000			$ 1,000,478,000

[1] Represents the unamortized portion of deferred gains realized upon termination of interest rate swaps in 2002 that were accounted for as fair value hedges. The gains are being amortized as a reduction of interest expense over the term of the notes

[2] Due December 2011.