Commitments and Contingencies (Details)	Sep. 30, 2013 Employee
Employee Contracts [Abstract]
Number of employees covered under union agreement	449
Number of union employees locked out	140

The company exercised its right to lockout union employees from its Canadian facility.

No definition available.

Name:	gsm_NumberOfUnionEmployeesLockedOut
Namespace Prefix:	gsm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant