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ACQUISITION - Additional Information (Detail) (Kemmerer Mine, USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jan. 31, 2012
Kemmerer Mine
Business Acquisition [Line Items]
Purchase price allocation of deferred revenue			$ 2.2
Expected increase in revenues and operating income		1.3
Deferred revenue	$ 0.9

This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to financial liabilities assumed in connection with a business combination for which the initial accounting was incomplete.

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