DEBT (Summary of Standby Letters Of Credit) (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Line of Credit Facility [Line Items]
Reclamation/restoration requirements	$ 220,581,000	$ 226,594,000	$ 238,689,000	$ 226,565,000
Standby Letters of Credit [Member]
Line of Credit Facility [Line Items]
Risk management insurance	34,111,000
Reclamation/restoration requirements	5,753,000
Total	$ 39,864,000