Loss Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Sep. 30, 2013	Sep. 30, 2012
Basic (loss) earnings per share computation - numerator [Abstract]
Net (loss) income attributable to Globe Specialty Metals, Inc.	$ (6,852)	$ (5,705)
Basic (loss) earnings per share computation - denominator [Abstract]
Weighted average basic shares outstanding (in shares)	75,310,143	75,050,560
Basic (loss) earnings per common share (in dollars per share)	$ (0.09)	$ (0.08)
Diluted (loss) earnings per share computation - numerator [Abstract]
Net (loss) income attributable to Globe Specialty Metals, Inc.	$ (6,852)	$ (5,705)
Diluted (loss) earnings per share computation - denominator [Abstract]
Weighted average basic shares outstanding (in shares)	75,310,143	75,050,560
Effect of dilutive securities (in shares)	0	0
Weighted average diluted shares outstanding (in shares)	75,310,143	75,050,560
Diluted (loss) earnings per common share (in dollars per share)	$ (0.09)	$ (0.08)
Stock Options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive shares (in shares)	227,874	208,578

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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