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	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract]
Asset retirement obligations, beginning of period (including current portion)	$ 279,864	$ 263,847
Accretion	23,329	16,426
Liabilities settled	(18,759)	(17,072)
ARO acquired	102,075	0
Changes due to foreign currency translation	(1,702)	0
Asset retirement obligations, end of period	384,807	263,201
Less current portion	(29,529)	(25,038)	(23,353)
Asset retirement obligations, less current portion	$ 355,278	$ 238,163	$ 256,511