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Intangible Assets - Summary of Intangible Assets (Detail) (USD $)
In Thousands, unless otherwise specified |
Dec. 31, 2014
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Mar. 31, 2014
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| Schedule Of Intangible Assets [Line Items] | ||
| Finite-Lived Intangible Assets, Gross Carrying Amount | $ 2,870us-gaap_FiniteLivedIntangibleAssetsGross | $ 2,870us-gaap_FiniteLivedIntangibleAssetsGross |
| Finite-Lived Intangible Assets, Accumulated Amortization | 897us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization | 762us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization |
| Finite-Lived Intangible Assets, Net Carrying Amount | 1,973us-gaap_FiniteLivedIntangibleAssetsNet | 2,108us-gaap_FiniteLivedIntangibleAssetsNet |
| Indefinite Lived Intangible Assets, Net Carrying Amount | 12,800us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill | 12,800us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill |
| Backlog [Member] | ||
| Schedule Of Intangible Assets [Line Items] | ||
| Finite-Lived Intangible Assets, Gross Carrying Amount |
170us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OrderOrProductionBacklogMember |
170us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OrderOrProductionBacklogMember |
| Finite-Lived Intangible Assets, Accumulated Amortization |
170us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OrderOrProductionBacklogMember |
170us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OrderOrProductionBacklogMember |
| Finite-Lived Intangible Assets, Net Carrying Amount |
0us-gaap_FiniteLivedIntangibleAssetsNet / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OrderOrProductionBacklogMember |
0us-gaap_FiniteLivedIntangibleAssetsNet / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OrderOrProductionBacklogMember |
| Customer Relationships [Member] | ||
| Schedule Of Intangible Assets [Line Items] | ||
| Finite-Lived Intangible Assets, Gross Carrying Amount |
2,700us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember |
2,700us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember |
| Finite-Lived Intangible Assets, Accumulated Amortization |
727us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember |
592us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember |
| Finite-Lived Intangible Assets, Net Carrying Amount |
1,973us-gaap_FiniteLivedIntangibleAssetsNet / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember |
2,108us-gaap_FiniteLivedIntangibleAssetsNet / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CustomerRelationshipsMember |
| Permits [Member] | ||
| Schedule Of Intangible Assets [Line Items] | ||
| Indefinite Lived Intangible Assets, Net Carrying Amount |
10,300us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = ghm_NuclearPermitsMember |
10,300us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = ghm_NuclearPermitsMember |
| Tradename [Member] | ||
| Schedule Of Intangible Assets [Line Items] | ||
| Indefinite Lived Intangible Assets, Net Carrying Amount |
$ 2,500us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |
$ 2,500us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill / us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_TradeNamesMember |
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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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