ASSET RETIREMENT OBLIGATIONS, CONTRACTUAL THIRD-PARTY RECLAMATION RECEIVABLES, AND RECLAMATION DEPOSITS - Changes in Company's Asset Retirement Obligations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract]
Asset retirement obligations, beginning of period (including current portion)	$ 279,864	$ 263,847
Accretion	5,836	5,481
Liabilities settled	(4,437)	(5,839)
Asset retirement obligations, end of period	281,263	263,489
Less current portion	(22,227)	(23,154)	(23,353)
Asset retirement obligations, less current portion	$ 259,036	$ 240,335	$ 256,511