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Stock-Based Compensation - Additional Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified | 3 Months Ended | 9 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013
Employee Stock Purchase Plan [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Stock based compensation expense | $ 16 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember | $ 14 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember | $ 46 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember | $ 42 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember
Income tax benefit to stock based compensation | 6 us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember | 5 us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember | 16 us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember | 14 us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember
Discounted purchase price of common stock percentage on fair market value | 85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember | 85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember | 85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember | 85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember
Shares approved for purchase under ESPP | 200,000 ghm_SharesAvailableUnderEmployeeStockPurchasePlan / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember |  | 200,000 ghm_SharesAvailableUnderEmployeeStockPurchasePlan / us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis = ghm_EmployeeStockPurchasePlanMember |
Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Stock based compensation expense | 166 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | 134 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | 435 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | 447 us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember
Income tax benefit to stock based compensation | $ 59 us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 47 us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 153 us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember | $ 157 us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember
Amended and Restated 2000 Incentive Plan [Member] | Employee Stock Option [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Stock options maximum term | 10 years | 10 years | 10 years | 10 years
Stock option awards granted | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember
Amended and Restated 2000 Incentive Plan [Member] | Employee Stock Option [Member] | Maximum [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of shares authorized | 1,375,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  | 1,375,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_AwardTypeAxis = us-gaap_EmployeeStockOptionMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_RangeAxis = us-gaap_MaximumMember |
Amended and Restated 2000 Incentive Plan [Member] | Restricted Stock [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Restricted stock awards | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember | 0 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember | 30,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember | 32,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember
Amended and Restated 2000 Incentive Plan [Member] | Restricted Stock [Member] | Time Vested Restricted Stock [Member] | Director [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Restricted stock awards |  |  | 7,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember / us-gaap_VestingAxis = ghm_TimeVestedRestrictedStockMember | 6,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember / us-gaap_VestingAxis = ghm_TimeVestedRestrictedStockMember
Share-based compensation vesting percentage |  |  | 100.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember / us-gaap_VestingAxis = ghm_TimeVestedRestrictedStockMember | 100.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_DirectorMember / us-gaap_VestingAxis = ghm_TimeVestedRestrictedStockMember
Vesting period |  |  | 1 year | 1 year
Amended and Restated 2000 Incentive Plan [Member] | Restricted Stock [Member] | Time Vested Restricted Stock [Member] | Officers and Key Employees [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Restricted stock awards |  |  | 11,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = ghm_OfficersAndKeyEmployeesMember / us-gaap_VestingAxis = ghm_TimeVestedRestrictedStockMember | 12,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = ghm_OfficersAndKeyEmployeesMember / us-gaap_VestingAxis = ghm_TimeVestedRestrictedStockMember
Share-based compensation vesting percentage |  |  | 33.33%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = ghm_OfficersAndKeyEmployeesMember / us-gaap_VestingAxis = ghm_TimeVestedRestrictedStockMember | 33.33%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = ghm_OfficersAndKeyEmployeesMember / us-gaap_VestingAxis = ghm_TimeVestedRestrictedStockMember
Vesting period |  |  | 3 years | 3 years
Amended and Restated 2000 Incentive Plan [Member] | Restricted Stock [Member] | Performance Vested Restricted Stock [Member] | Officer [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Restricted stock awards |  |  | 12,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_OfficerMember / us-gaap_VestingAxis = ghm_PerformanceVestedRestrictedStockMember | 14,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_OfficerMember / us-gaap_VestingAxis = ghm_PerformanceVestedRestrictedStockMember
Share-based compensation vesting percentage |  |  | 100.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_OfficerMember / us-gaap_VestingAxis = ghm_PerformanceVestedRestrictedStockMember | 100.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_TitleOfIndividualAxis = us-gaap_OfficerMember / us-gaap_VestingAxis = ghm_PerformanceVestedRestrictedStockMember
Vesting period |  |  | 3 years | 3 years
Amended and Restated 2000 Incentive Plan [Member] | Restricted Stock [Member] | Maximum [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of shares authorized | 250,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  | 250,000 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockMember / us-gaap_PlanNameAxis = ghm_AmendedAndRestated2000IncentivePlanMember / us-gaap_RangeAxis = us-gaap_MaximumMember |

X
- Definition Maximum number of shares originally approved for purchase by employees under the employee stock purchase plan. + References No definition available. + Details
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 14 -Section F + Details
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- Definition The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Percentage of vesting of share-based compensation awards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Definition Gross number of share options (or share units) granted during the period. + References No definition available. + Details
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- Definition Purchase price of common stock expressed as a percentage of its fair value. + References No definition available. + Details
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