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	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract]
Asset retirement obligations, beginning of period (including current portion)	$ 279,864	$ 263,847
Accretion	14,003	10,951
Liabilities settled	(10,250)	(11,647)
ARO acquired	102,075	0
Changes due to foreign currency translation	3,692	0
Asset retirement obligations, end of period	389,384	263,151
Less current portion	(31,131)	(24,105)	(23,353)
Asset retirement obligations, less current portion	$ 358,253	$ 239,046	$ 256,511