FAIR VALUE MEASUREMENTS (Details 2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Fair value and carrying value of financial instruments
Derivative instruments assets	$ 129,500
Derivative instruments liabilities	53,100
Credit Facility	215,000		105,000
Credit Facility, Fair Value	215,000	[1]	105,000
8 1/2% Senior Notes due 2014
Fair value and carrying value of financial instruments
Notes payable, carrying value	589,062		587,611
Notes payable, fair value	642,000	[1]	653,250	[1]
Interest rate (as a percent)	8.50%		8.50%
7 1/4% Senior Notes due 2019
Fair value and carrying value of financial instruments
Notes payable, carrying value	1,000,407		1,000,421
Notes payable, fair value	985,000	[1]	1,025,000	[1]
Interest rate (as a percent)	7.25%		7.25%
Carrying Amount
Fair value and carrying value of financial instruments
Derivative instruments assets	129,540		100,043
Derivative instruments liabilities	53,130		28,944
Fair Value
Fair value and carrying value of financial instruments
Derivative instruments assets	129,540	[1]	100,043	[1]
Derivative instruments liabilities	53,130	[1]	28,944	[1]
Using Quoted Prices in Active Markets for Identical Assets (Level 1) | 8 1/2% Senior Notes due 2014
Fair value and carrying value of financial instruments
Notes payable, fair value	642,000
Using Quoted Prices in Active Markets for Identical Assets (Level 1) | 7 1/4% Senior Notes due 2019
Fair value and carrying value of financial instruments
Notes payable, fair value	985,000
Using Significant Other Observable Inputs (Level 2)
Fair value and carrying value of financial instruments
Credit Facility, Fair Value	215,000
Using Significant Other Observable Inputs (Level 2) | Fair Value
Fair value and carrying value of financial instruments
Derivative instruments assets	129,540
Derivative instruments liabilities	$ 53,130

[1] The Company used various assumptions and methods in estimating the fair values of its financial instruments. The fair values of the senior notes were estimated based on quoted market prices. The carrying amount of the credit facility approximated fair value due to the short original maturities of the borrowings and because the borrowings bear interest at variable market rates. The methods used to determine the fair values of the derivative instruments are discussed above. See also Note 8 for more information on the derivative instruments.