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Segment Information - Net Sales by Product Line (Detail) (USD $) In Thousands, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2015 | Mar. 31, 2014 | Mar. 31, 2013
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales | $ 37,455 us-gaap_SalesRevenueNet | $ 33,646 us-gaap_SalesRevenueNet | $ 35,566 us-gaap_SalesRevenueNet | $ 28,502 us-gaap_SalesRevenueNet | $ 26,087 us-gaap_SalesRevenueNet | $ 23,385 us-gaap_SalesRevenueNet | $ 24,490 us-gaap_SalesRevenueNet | $ 28,256 us-gaap_SalesRevenueNet | $ 135,169 us-gaap_SalesRevenueNet | $ 102,218 us-gaap_SalesRevenueNet | $ 104,973 us-gaap_SalesRevenueNet
Heat transfer equipment [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 58,224 us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = ghm_HeatTransferEquipmentMember | 37,086 us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = ghm_HeatTransferEquipmentMember | 43,764 us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = ghm_HeatTransferEquipmentMember
Vacuum equipment [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | 28,698 us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = ghm_VacuumEquipmentMember | 27,236 us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = ghm_VacuumEquipmentMember | 22,891 us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = ghm_VacuumEquipmentMember
All other [Member] |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net sales |  |  |  |  |  |  |  |  | $ 48,247 us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = ghm_AllOtherProductLinesMember | $ 37,896 us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = ghm_AllOtherProductLinesMember | $ 38,318 us-gaap_SalesRevenueNet / us-gaap_ProductOrServiceAxis = ghm_AllOtherProductLinesMember

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- Definition Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Article 5 + Details
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- Details
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