ASSET RETIREMENT OBLIGATIONS (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Activity affecting the asset retirement and mine closing liability:
Balance at the beginning of the period	$ 84,836	$ 72,342
Accretion expense	3,004	2,853
Payments	(2,242)	(2,842)
Allocation of liability associated with acquisition, mine development and change in assumptions	(2,700)	12,483
Balance at the end of the period	$ 82,898	$ 84,836