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The Company and Its Accounting Policies - Summary of Costs and Estimated Earnings on Contracts (Detail) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Mar. 31, 2014
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Accounting Policies [Abstract] |  |
Costs incurred since inception on contracts in progress | $ 64,912 ghm_CostOnContractInProgress | $ 42,019 ghm_CostOnContractInProgress
Estimated earnings since inception on contracts in progress | 16,067 ghm_EstimatedEarningsOnContractInProgress | 10,208 ghm_EstimatedEarningsOnContractInProgress
Costs and estimated earnings | 80,979 ghm_CostAndEstimatedEarningsOnContractInProgress | 52,227 ghm_CostAndEstimatedEarningsOnContractInProgress
Less billings to date | 69,636 ghm_BillingsToDate | 57,489 ghm_BillingsToDate
Net under (over) billings | 11,343 us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear |
Net under (over) billings |  | $ (5,262)us-gaap_BillingsInExcessOfCostCurrent

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- Definition Aggregate amount of billings to customers for contracts in process since the inception of the contracts. + References No definition available. + Details
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- Definition The total amount that has been or will be billed to customers on all contracts in process. + References No definition available. + Details
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- Definition Liability attributable to (i) billings in excess of costs under the percentage of completion contract accounting method representing the difference between contractually invoiced amounts (billings) and revenue recognized based, for example, on costs incurred to estimated total costs at period end or (ii) contractually invoiced amounts (billings) in excess of costs incurred and accumulated under the completed contract accounting method that are expected to be realized within one year or one operating cycle, whichever is longer, from the reporting date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57788-111642 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57807-111642 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57795-111642 + Details
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- Definition Amount of receivable reflecting the cost incurred on uncompleted contracts in excess of related billings which is expected to be collected within one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57807-111642 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 605 -SubTopic 35 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57795-111642 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3(c)(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Subparagraph c(3) -Article 5 + Details
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