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Revenue Recognition - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 9 Months Ended
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Dec. 31, 2013
Revenue Recognition [Line Items] |
Company recognizes planned manufacturing process | 28 days
Direct labor hours worked on contracts | 0 days 575 hours
Reserve for credit losses related to unbilled revenue | $ 0
Minimum [Member] |
Revenue Recognition [Line Items] |
Substantial completion of manufacturing process | 95.00%

X
- Definition Planned manufacturing process used in determining the applicable revenue recognition method. + References No definition available. + Details
Name: | ghm_CompanyRecognizesPlannedManufacturingProcess
Namespace Prefix: | ghm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Credit loss related to unbilled revenue. + References No definition available. + Details
Name: | ghm_CreditLossRelatedToUnbilledRevenue
Namespace Prefix: | ghm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Equivalent of four weeks of direct labor hours worked on contracts. + References No definition available. + Details
Name: | ghm_DirectLaborPeriodWorkedOnContracts
Namespace Prefix: | ghm_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | ghm_RevenueRecognitionLineItems
Namespace Prefix: | ghm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percent at which the manufacturing process of a contract must be completed with regard to direct labor hours for the contract to be considered substantially complete. + References No definition available. + Details
Name: | ghm_SubstantialCompletionOfManufacturingProcess
Namespace Prefix: | ghm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration