DEBT (Bank Credit Facility) (Details) (USD $)			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Credit Facility	Feb. 15, 2013 Credit Facility	Dec. 31, 2012 Credit Facility	Apr. 12, 2013 Credit Facility Subsequent Event
Bank Credit Facility
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
Credit Facility maximum borrowing capacity optional expansion			1,800,000,000
Borrowing base under the Credit Facility			900,000,000			900,000,000
Credit Facility borrowing capacity reduction as percentage of the stated principal amount of issued senior notes (as a percent)			25.00%
Credit Facility borrowing capacity reduction due to sale of properties with value in excess of this percentage of the borrowing base then in effect (as a percent)			10.00%
Credit Facility borrowing base reduction due to sale of properties				170,000,000
Credit Facility collateral as percentage of present value of the estimated proved oil and gas properties and related assets (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	140,000,000	65,000,000	140,000,000		65,000,000
Credit Facility weighted average interest rate			1.80%
Credit Facility outstanding letters of credit			1,600,000
Credit facility unused borrowing amount			$ 758,400,000