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Quarterly Financial Data (Unaudited) - Summary of Company's Unaudited Quarterly Results (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Mar. 31, 2015
Quarterly Financial Information Disclosure [Abstract] |
Restructuring charge | $ 1,718 us-gaap_RestructuringAndRelatedCostIncurredCost
Restructuring charge, net of tax | $ 1,164 ghm_RestructuringAndRelatedCostIncurredCostNetOfTax

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- Definition Restructuring and related cost incurred cost net of tax. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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

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- Definition Discloses the amount charged against the accrued restructuring reserves, or earnings if not previously accrued, during the period for the specified type of restructuring cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section P -Subsection 3, 4 + Details
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Period Type: | duration