RECLAMATION PROVISION AND OTHER LIABILITIES (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Basic defined contribution pension plan
Defined contribution plan
Employer contribution to defined contribution plan, percentage of base employment compensation	5.00%
Defined contribution pension plan amount contributed	$ 11.9	$ 10.7	$ 8.8
Supplemental defined contribution pension plan
Defined contribution plan
Additional contribution by employer to defined contribution plan (as a percent)	10.00%
Defined contribution pension plan amount contributed	$ 0.8	$ 0.9	$ 1.1

The amount of the cost recognized during the period for defined contribution plans.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 11

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration