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Employee Benefit Plans - Additional Information (Detail) (USD $) Share data in Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Mar. 31, 2015 | Mar. 31, 2014 | Mar. 31, 2013
Defined Benefit Plan Disclosure [Line Items] |  |  |
Employee's years of service and average earnings | Five highest consecutive calendar years of compensation in the ten-year period preceding retirement |  |
Percentage of blue collar employees | 50.00%ghm_PercentageOfBlueCollarEmployees |  |
Increase in projected benefit obligations | $ 2,145,000 ghm_DefinedBenefitPlanIncreaseInProjectedBenefitObligation |  |
Accumulated benefit obligation | 33,998,000 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation | 28,254,000 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation |
Employer contribution description | Matching contributions equal to 100% of the first 3% of an employee's salary deferral and 50% of the next 2% percent of an employee's salary deferral |  |
Contribution equal to employee salary deferral | 100.00%ghm_DefinedContributionPlanEmployerMatchingPercentOnFirstThreePercentEmployeeSalaryDeferral |  |
Contribution next to employee salary deferral | 3.00%ghm_DefinedContributionPlanSalaryDeferralPercentageThatReceivesEquivalentCompanyMatch |  |
Contribution for additional employee salary deferral | 50.00%ghm_DefinedAdditionalContributionPlanEmployerMatchingContributionPercent |  |
Contribution additional next to employee salary deferral | 2.00%ghm_DefinedContributionPlanSalaryDeferralPercentageThatReceivesAdditionalCompanyMatch |  |
Share of the medical premium cost for family coverage | 4,000 ghm_CompanyShareOfMedicalPremiumCostForEarlyRetireeFamilyCoverageUnderOtherPostretirementPlan |  |
Share of the medical premium cost for single coverage | 2,000 ghm_CompanyShareOfMedicalPremiumCostForEarlyRetireeSingleCoverageUnderOtherPostretirementPlan |  |
Share of the medical premium both family and single coverage for regular retirees | 1,000 ghm_CompanyShareOfMedicalPremiumCostForRegularRetireeCoverageUnderOtherPostretirementPlan |  |
Medical care cost trend rate | 5.00%us-gaap_DefinedBenefitPlanUltimateHealthCareCostTrendRate |  |
Medical care trend year | 2021 |  |
Medical care cost trend rate decrements | 0.50%ghm_DefinedBenefitPlanDecrementInHealthCareCostTrendRate |  |
Current portion of accrued postretirement benefit obligation | 92,000 ghm_AccruedPostretirementBenefitLiabilityCurrent | 98,000 ghm_AccruedPostretirementBenefitLiabilityCurrent |
Employee stock ownership plan, shares | 233 us-gaap_EmployeeStockOwnershipPlanESOPSharesInESOP | 252 us-gaap_EmployeeStockOwnershipPlanESOPSharesInESOP |
Company contributions to the ESOP | 0 us-gaap_EmployeeStockOwnershipPlanESOPCashContributionsToESOP | 0 us-gaap_EmployeeStockOwnershipPlanESOPCashContributionsToESOP | 0 us-gaap_EmployeeStockOwnershipPlanESOPCashContributionsToESOP
Stop loss coverage per employee for claims | 100,000 ghm_SpecificStopLossInsuranceCoveragePerEmployee |  |
Maximum aggregate stop loss coverage | 1,000,000 ghm_AggregateStopLossInsuranceCoveragePerEmployee |  |
Total plan amount | 3,738,000 ghm_AnnualPlanAggregateStopLossInsuranceCoverage |  |
Self-Insured medical plan liability | 446,000 ghm_SelfInsuredMedicalPlanLiability | 221,000 ghm_SelfInsuredMedicalPlanLiability |
Defined Contribution Plan 401K [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Contributions to defined contribution plan | 940,000 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_PlanNameAxis = ghm_DefinedContributionPlan401kMember | 831,000 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_PlanNameAxis = ghm_DefinedContributionPlan401kMember | 753,000 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_PlanNameAxis = ghm_DefinedContributionPlan401kMember
Pension Plans, Defined Benefit [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Estimated net actuarial loss for pension plan | 1,174,000 us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |
Estimated prior service cost for pension plan | 0 us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember |  |
Pension expense | (469,000)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 213,000 us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 248,000 us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Weighted average discount rate used to develop net postretirement benefit cost | 4.46%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 4.28%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember | 4.76%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember
Defined Contribution Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Contributions to defined contribution plan | 294,000 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = ghm_DefinedContributionPlanMember | 257,000 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = ghm_DefinedContributionPlanMember | 204,000 us-gaap_DefinedContributionPlanCostRecognized / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = ghm_DefinedContributionPlanMember
Supplemental Executive Retirement Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Pension expense | 70,000 us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 70,000 us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 24,000 us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Pension expense related liability | 341,000 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 298,000 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesCurrentAndNoncurrent / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |
Current portion of the related liability included in accrued compensation | 26,000 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember | 26,000 us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember |
Other Postretirement Benefit Plans [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Estimated net actuarial loss for pension plan | 38,000 us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |
Estimated prior service cost for pension plan | 0 us-gaap_DefinedBenefitPlanFutureAmortizationOfPriorServiceCostCredit / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember |  |
Pension expense | $ (40,000)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | $ (87,000)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | $ (83,000)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Weighted average discount rate used to develop net postretirement benefit cost | 3.59%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 3.26%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember | 3.96%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember

X
- Definition Current portion of the accrued postretirement liability recorded in the consolidated balance sheet. + References No definition available. + Details
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Balance Type: | credit
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X
- Definition Aggregate annual stop loss coverage amount per employee for claims incurred. + References No definition available. + Details
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Balance Type: | na
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- Definition Aggregate annual stop loss coverage for the entire medical plan. + References No definition available. + Details
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- Definition Company's share of the medical premium cost for early retirees for family coverage under the other postretirement plan. + References No definition available. + Details
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- Definition Company's share of the medical premium cost for early retirees for single coverage under the other postretirement plan. + References No definition available. + Details
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- Definition Company's share of the medical premium cost for regular retirees for coverage under the other postretirement plan. + References No definition available. + Details
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- Definition The employer matching contribution percentage on the 2% employee salary deferral after the first 3% employee salary deferral. + References No definition available. + Details
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- Definition Average earnings description for calculation of benefits. + References No definition available. + Details
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- Definition Annual decrement percentage in the defined benefit plan health care cost trend rate used to reach the ultimate health care cost trend rate. + References No definition available. + Details
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- Definition The increase in the defined benefit pension plan projected benefit obligation resulting from a change in the mortality table assumption. + References No definition available. + Details
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- Definition Percentage of employee's first 3% salary deferral for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
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- Definition The employee deferral percentage that receives a 50% employer matching contribution. + References No definition available. + Details
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- Definition The employee salary deferral that receives 100% matching company contribution. + References No definition available. + Details
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- Definition Description of employer matching contributions to the 401K plan. + References No definition available. + Details
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- Definition The weighting in the mortality table assumption for male blue collar workers used in developing the defined benefit pension plan projected benefit obligation. + References No definition available. + Details
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- Definition The liability recognized in the balance sheet that is associated with the self insured medical plan. + References No definition available. + Details
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- Definition Stop loss coverage amount per employee for each specific claim incurred. + References No definition available. + Details
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- Definition For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Accumulated Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6503844 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The interest rate used to adjust for the time value of money. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Details
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- Definition Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position. + References No definition available. + Details
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- Definition Amount included in accumulated other comprehensive income (AOCI) related to prior service cost (credit) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position. + References No definition available. + Details
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- Definition The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The ultimate trend rate for health care costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Year the ultimate health care cost trend rate is expected to be reached, in CCYY format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition The amount of the cost recognized during the period for defined contribution plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942 + Details
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- Definition This item represents the amount of cash contributions during the period made by the entity to the Employee Stock Ownership Plan (ESOP). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 40 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929 + Details
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- Definition Sum of the allocated, committed-to-be-released and suspense shares of the entity held by the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 40 -Section 50 -Paragraph 1 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=6418621&loc=d3e17540-113929 + Details
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- Definition For a classified balance sheet, the amount recognized in balance sheet as a current liability associated with an underfunded defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Current Liabilities -URI http://asc.fasb.org/extlink&oid=6509677 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=21915240&loc=d3e1703-114919 + Details
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- Definition This represents the entire liability recognized in the balance sheet that is associated with the defined benefit plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.15) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.15) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2417-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2410-114920 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=21915240&loc=d3e1703-114919 + Details
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