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Product Warranty Liability - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 9 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013
Guarantees [Abstract] |  |  |  |
Income for product warranties | $ 436 ghm_ProductWarrantyIncomeExpense | $ (47)ghm_ProductWarrantyIncomeExpense | $ 573 ghm_ProductWarrantyIncomeExpense | $ 11 ghm_ProductWarrantyIncomeExpense

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- 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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- Details
Name: | us-gaap_GuaranteesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration