Business Combinations, Investments, and Divestitures (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended				0 Months Ended	12 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2010	Mar. 31, 2011	Nov. 05, 2009 Globe Metais [Member]	Jun. 30, 2010 WVA LLC [Member] Mg	Nov. 05, 2009 WVA LLC [Member]	Jun. 30, 2010 Masterloy [Member]	Dec. 31, 2010 Fluorita de Mexico, S.A. de C.V. (FDM) [Member]	Mar. 31, 2011 Core Metals [Member]	Jun. 30, 2011 Alden Resources, LLC [Member]	Jun. 30, 2012 Quebec Silicon Limited Partnership [Member]	Jun. 30, 2012 Globe Specialty Metals [Member] Quebec Silicon Limited Partnership [Member]	Jun. 30, 2012 Dow Corning [Member] Quebec Silicon Limited Partnership [Member]
Business Acquisition [Abstract]
Percentage of interest acquired (in hundredths)											100.00%	51.00%
Purchase price											$ 73,200
Purchase price, cash paid										52,000	18,200	8,803
Purchase price, earn-out payment											6,800
Purchase price, financed with revolving credit facility										15,329		31,800
Revolving credit facility face value	300,000											300,000
Purchase price, financed with bank debt											55,000
Goodwill recorded										1,274		3,062
Right to purchase the plant's output (in hundredths)													51.00%	49.00%
Business Divestiture [Abstract]
Business Divestiture, Percentage of Business Sold					100.00%		49.00%		49.00%
Cash received in disposition					65,600			3,000
Business Divestiture, Sale Price					75,000		100,000		2,500
Business Divestiture, Cash Balances Assumed by Acquirer					16,555
Business Divestiture, Liabilities Assumed by Aquirer					14,000
Amount of Silicon Metal Required to be Sold						20,000
Business Divestiture, Transaction Costs							2,146
Provision for income taxes	28,760	35,988	20,539			26,575
Increase in noncontrolling interest recorded as increase in additional paid-in capital	210		71,409			44,397
Nigerian Mining Licenses [Abstract]
Advance payments to acquire exploration mining licenses in Nigeria				$ 17,000