Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation - Additional Information (Detail)

v2.4.1.9
Stock-Based Compensation - Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended 9 Months Ended
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 $ 16us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= ghm_EmployeeStockPurchasePlanMember 		$ 14us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= ghm_EmployeeStockPurchasePlanMember 		$ 46us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= ghm_EmployeeStockPurchasePlanMember 		$ 42us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= ghm_EmployeeStockPurchasePlanMember
Income tax benefit to stock based compensation 6us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= ghm_EmployeeStockPurchasePlanMember 		5us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= ghm_EmployeeStockPurchasePlanMember 		16us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= ghm_EmployeeStockPurchasePlanMember 		14us-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 200,000ghm_SharesAvailableUnderEmployeeStockPurchasePlan
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= ghm_EmployeeStockPurchasePlanMember 		  200,000ghm_SharesAvailableUnderEmployeeStockPurchasePlan
/ us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis
= ghm_EmployeeStockPurchasePlanMember 		 
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock based compensation expense 166us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		134us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		435us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		447us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Income tax benefit to stock based compensation $ 59us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		$ 47us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		$ 153us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember 		$ 157us-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 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember 		0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember 		0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember 		0us-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 1,375,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		  1,375,000us-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 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember 		0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember 		30,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember 		32,000us-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     7,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
/ us-gaap_VestingAxis
= ghm_TimeVestedRestrictedStockMember 		6,000us-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     11,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= ghm_OfficersAndKeyEmployeesMember
/ us-gaap_VestingAxis
= ghm_TimeVestedRestrictedStockMember 		12,000us-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     12,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember
/ us-gaap_VestingAxis
= ghm_PerformanceVestedRestrictedStockMember 		14,000us-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 250,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember 		  250,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember