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v3.3.1.900

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

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