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Other Income - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Dec. 31, 2015	Dec. 31, 2015
Other Income And Expenses [Abstract]
Other income	$ 1,784	$ 1,784

X

- Definition

Cancellation fee income earned from customers due to the cancellation of orders by customers.

+ References

No definition available.

+ Details

Name:	ghm_CancellationFeeIncome
Namespace Prefix:	ghm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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- References

No definition available.

+ Details

Name:	us-gaap_OtherIncomeAndExpensesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration