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Financial Instruments and Derivative Financial Instrument - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2014 | Mar. 31, 2013
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Financial Instruments And Fair Value Measurements [Line Items] |  |
Letters of credit outstanding, amount | $ 15,473 | $ 12,354
Backlog [Member] | Customer One [Member] |  |
Financial Instruments And Fair Value Measurements [Line Items] |  |
Concentration of risk percentage for backlog as of the balance sheet date | 13.00% | 21.00%
Backlog [Member] | Customer Two [Member] |  |
Financial Instruments And Fair Value Measurements [Line Items] |  |
Concentration of risk percentage for backlog as of the balance sheet date | 12.00% | 12.00%

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- Definition Concentration of risk percentage. + References No definition available. + Details
Name: | ghm_ConcentrationOfRiskPercentage
Namespace Prefix: | ghm_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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

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- Definition The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. + References No definition available. + Details
Name: | us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant