DEBT (Details) (USD $)	3 Months Ended
	Jun. 30, 2012		Dec. 31, 2011
Debt
Credit Facility	$ 348,000,000		$ 105,000,000
Total Debt
Debt, Principal	1,948,012,000		1,705,012,000
Debt, Unamortized Premium (Discount)	(9,094,000)		(11,968,000)
Total debt	1,938,918,000		1,693,044,000
Less: current portion of debt
Current portion of debt	(12,000)		0
Long-term portion of debt
Long-term portion of debt, principal	1,948,000,000		1,705,012,000
Long-term portion of debt, unamortized premium (discount)	(9,094,000)		(11,968,000)
Long-term portion of debt	1,938,906,000		1,693,044,000
Credit Facility
Debt
Credit Facility	348,000,000		105,000,000
Total Debt
Debt, Unamortized Premium (Discount)	0		0
Credit Facility
Maximum borrowing capacity	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 Facility	1,250,000,000
Credit Facility collateral as percentage of present value of oil and gas properties (as a percent)	75.00%
Credit Facility covenant based on ratio of total debt outstanding to EBITDA, Numerator	4.5
Credit Facility covenant based on ratio of total debt outstanding to EBITDA, Denominator	1.0
Credit Facility weighted average interest rate (as a percent)	2.00%
Outstanding letters of credit	1,800,000
Credit Facility unused borrowing amount	900,200,000
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
Total debt	12,000		12,000
Less: current portion of debt
Less: current portion of debt, principal	(12,000)	[1]	0	[1]
Less: current portion of debt, unamortized premium (discount)	0	[1]	0	[1]
Current portion of debt	(12,000)	[1]	0	[1]
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)	(9,487,000)		(12,389,000)
Total debt	590,513,000		587,611,000
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)	393,000		421,000
Total debt	$ 1,000,393,000		$ 1,000,421,000

[1] Due June 2013.