Intangible Assets (Tables)	3 Months Ended
Jun. 30, 2013
Intangible Assets [Abstract]
Summary of intangible assets	Summary of intangible assets

Tabular disclosure of assets, excluding financial assets and goodwill, lacking physical substance with a finite and indefinite life, by major class.

No definition available.

Name:	ghm_ScheduleOfIntangibleAssetsAndAccumulatedAmortizationTableTextBlock
Namespace Prefix:	ghm_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration