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Income Taxes - Components of Income Before Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2012
Income Taxes [Line Items] |  |  |
Income before income taxes, total | $ 14,710 | $ 15,577 | $ 16,677
U.S. [Member] |  |  |
Income Taxes [Line Items] |  |  |
Income before income taxes, total | 14,127 | 14,597 | 16,708
China [Member] |  |  |
Income Taxes [Line Items] |  |  |
Income before income taxes, total | $ 583 | $ 980 | $ (31)

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

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- Definition This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 10 -Article 5 + Details
Name: | us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration