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Product Warranty Liability - Additional Information (Detail) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2015 | Dec. 31, 2014
Guarantees [Abstract] |  |  |  |
Income (expense) for product warranties | $ 158 | $ (436) | $ 45 | $ (573)

X
- Definition 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. + References No definition available. + Details
Name: | ghm_ProductWarrantyIncomeExpense
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_GuaranteesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration