DEFERRED REVENUE (Narrative) (Details) (USD $)	6 Months Ended	9 Months Ended
	Mar. 31, 2013	Sep. 30, 2013 T	Sep. 30, 2012	Dec. 31, 2012 T
Deferred Revenue Arrangement [Line Items]
Proceeds from sale of future production	$ 73,644,000	$ 153,095,000	$ 0
Volumetric production payment termination date		Sep. 30, 2051		Dec. 31, 2052
Volumetric production payment estimated percentage sold		11.50%		10.50%
Volumetric production payment estimated tons to be delivered		29,000,000		15,000,000
Minimum
Deferred Revenue Arrangement [Line Items]
Estimated deferred revenue to be recognized in the next 12 months		4,000,000
Maximum
Deferred Revenue Arrangement [Line Items]
Estimated deferred revenue to be recognized in the next 12 months		$ 5,000,000
Tons subject to volumetric production payment		250,800,000		143,200,000