Product Warranty Liability (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Jun. 30, 2013	Jun. 30, 2012
Product Warranty Liability (Textual) [Abstract]
Product warranties	$ 20	$ (11)

The (income) expense (included) charged (in) against earnings for the period pertaining to standard and extended warranties on the entity's goods and services granted to customers.

No definition available.

Name:	ghm_ProductWarrantyIncomeExpense
Namespace Prefix:	ghm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration