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The Company and Its Accounting Policies - Additional Information (Detail) (USD $) Share data in Thousands, unless otherwise specified | 12 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Mar. 31, 2013 | Jan. 29, 2015
Schedule Of Accounting Policies [Line Items] |  |  |  |
Company recognizes planned manufacturing process | 28 days |  |  |
Direct labor hours worked on contracts | 0 days 575 hours |  |  |
Receivables billed but not paid under retainage provisions in its customer contracts | $ 1,751,000 us-gaap_ContractReceivableRetainage | $ 901,000 us-gaap_ContractReceivableRetainage |  |
Minimum level of likelihood | 50.00%ghm_TestOfImpairmentMoreLikelihoodPercentage |  |  |
Research and development costs | 3,585,000 us-gaap_ResearchAndDevelopmentExpense | 3,436,000 us-gaap_ResearchAndDevelopmentExpense | 3,579,000 us-gaap_ResearchAndDevelopmentExpense |
Maximum stock authorized to purchase under stock repurchase program |  |  |  | 18,000,000 us-gaap_StockRepurchaseProgramAuthorizedAmount1
Antidilutive securities excluded from computation of earnings per share | 12 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount | 2 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount | 14 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount |
Interest paid | 11,000 us-gaap_InterestPaidNet | 12,000 us-gaap_InterestPaidNet | 59,000 us-gaap_InterestPaidNet |
Income taxes paid | 6,491,000 us-gaap_IncomeTaxesPaid | 3,302,000 us-gaap_IncomeTaxesPaid | 4,064,000 us-gaap_IncomeTaxesPaid |
Pension and other postretirement benefit adjustments, net of tax | 3,294,000 us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax | (2,275,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax | (92,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax |
Issuance of treasury stock | 325,000 us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued | 317,000 us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued | 297,000 us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued |
Capital expenditures | 174,000 us-gaap_CapitalExpendituresIncurredButNotYetPaid | 40,000 us-gaap_CapitalExpendituresIncurredButNotYetPaid | 142,000 us-gaap_CapitalExpendituresIncurredButNotYetPaid |
Capital leases | $ 22,000 us-gaap_CapitalLeaseObligationsIncurred | $ 90,000 us-gaap_CapitalLeaseObligationsIncurred | $ 11,000 us-gaap_CapitalLeaseObligationsIncurred |
Buildings and Leasehold Improvements [Member] |  |  |  |
Schedule Of Accounting Policies [Line Items] |  |  |  |
Estimated useful lives range | 40 years |  |  |
Customer Relationships [Member] |  |  |  |
Schedule Of Accounting Policies [Line Items] |  |  |  |
Estimated useful lives | 15 years |  |  |
Minimum [Member] |  |  |  |
Schedule Of Accounting Policies [Line Items] |  |  |  |
Substantial completion of manufacturing process | 95.00%ghm_SubstantialCompletionOfManufacturingProcess / us-gaap_RangeAxis = us-gaap_MinimumMember |  |  |
Treasury with original maturities period | 3 months |  |  |
Minimum [Member] | Office Equipment [Member] |  |  |  |
Schedule Of Accounting Policies [Line Items] |  |  |  |
Estimated useful lives range | 5 years |  |  |
Minimum [Member] | Manufacturing Equipment [Member] |  |  |  |
Schedule Of Accounting Policies [Line Items] |  |  |  |
Estimated useful lives range | 8 years |  |  |
Maximum [Member] |  |  |  |
Schedule Of Accounting Policies [Line Items] |  |  |  |
Investment maturity date range end | Feb. 10, 2016 |  |  |
Treasury with original maturities period | 1 year |  |  |
Maximum [Member] | Office Equipment [Member] |  |  |  |
Schedule Of Accounting Policies [Line Items] |  |  |  |
Estimated useful lives range | 8 years |  |  |
Maximum [Member] | Manufacturing Equipment [Member] |  |  |  |
Schedule Of Accounting Policies [Line Items] |  |  |  |
Estimated useful lives range | 25 years |  |  |

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