Earnings (Loss) Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Basic earnings per share computation - numerator [Abstract]
Net income attributable to Globe Specialty Metals, Inc.	$ (5,705)	$ 20,693
Basic earnings per share computation - denominator [Abstract]
Weighted average basic shares outstanding (in shares)	75,050,560	75,019,481
Basic earnings (loss) per common share (in dollars per share)	$ (0.08)	$ 0.28
Diluted earnings per share computation - numerator [Abstract]
Net income attributable to Globe Specialty Metals, Inc.	$ (5,705)	$ 20,693
Diluted earnings per share computation - denominator [Abstract]
Weighted average basic shares outstanding (in shares)	75,050,560	75,019,481
Effect of dilutive securities (in shares)	0	1,769,502
Weighted average diluted shares outstanding (in shares)	75,050,560	76,788,983
Diluted earnings per common share (in dollars per share)	$ (0.08)	$ 0.27
Antidilutive shares excluded from the computation of earnings per share (in shares)	208,578	1,052,122