Annual report pursuant to Section 13 and 15(d)

Stock Compensation Plans - Additional Information (Detail)

v2.4.1.9
Stock Compensation Plans - Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock option awards granted     49,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross  
Weighted average fair value of options granted     $ 4.97us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue  
Cash proceeds from the exercise of stock options $ 47us-gaap_ProceedsFromStockOptionsExercised $ 581us-gaap_ProceedsFromStockOptionsExercised $ 83us-gaap_ProceedsFromStockOptionsExercised  
Total intrinsic value of the stock options exercised 32us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue 1,221us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue 203us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue  
Unrecognized stock-based compensation expense 1,055us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized      
Weighted average period for recognize expense 1 year 5 months 9 days      
Options, stock awards and performance awards available for future grants 403,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant      
Stock Compensation Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock based compensation expense 598us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_StockCompensationPlanMember
582us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_StockCompensationPlanMember
524us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_StockCompensationPlanMember
 
Income tax benefit to stock based compensation 210us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_StockCompensationPlanMember
205us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_StockCompensationPlanMember
184us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_StockCompensationPlanMember
 
Increase in capital in excess of par value for the income tax benefit realized upon exercise of stock options and vesting of restricted 197us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities
/ us-gaap_AwardTypeAxis
= us-gaap_StockCompensationPlanMember
268us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities
/ us-gaap_AwardTypeAxis
= us-gaap_StockCompensationPlanMember
41us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities
/ us-gaap_AwardTypeAxis
= us-gaap_StockCompensationPlanMember
 
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock awarded 30,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
32,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
26,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
 
Employee Stock Option [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock options maximum term     10 years  
Stock option awards granted     49,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
 
Share-based compensation vesting percentage     33.33%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
 
Vesting period     3 years  
Amended and Restated 2000 Incentive Plan [Member] | Stock Compensation Plan [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_StockCompensationPlanMember
/ 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 awarded 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
26,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember
 
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]        
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    
Restricted stock awarded 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
18,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_OfficerMember
/ us-gaap_VestingAxis
= ghm_PerformanceVestedRestrictedStockMember
 
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]        
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    
Restricted stock awarded 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
   
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]        
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    
Restricted stock awarded 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
8,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
/ us-gaap_PlanNameAxis
= ghm_AmendedAndRestated2000IncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
/ us-gaap_VestingAxis
= ghm_TimeVestedRestrictedStockMember
 
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
     
Long Term Incentive Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Amounts paid to participant 157us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_PlanNameAxis
= ghm_LongTermIncentivePlanMember
     
Long Term Incentive Plan [Member] | Director [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Related liability recorded under plan 158us-gaap_DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent
/ us-gaap_PlanNameAxis
= ghm_LongTermIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
315us-gaap_DeferredCompensationSharebasedArrangementsLiabilityCurrentAndNoncurrent
/ us-gaap_PlanNameAxis
= ghm_LongTermIncentivePlanMember
/ us-gaap_TitleOfIndividualAxis
= us-gaap_DirectorMember
   
Long Term Incentive Plan [Member] | Subsequent Event [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Amounts paid to participant       158us-gaap_DeferredCompensationArrangementWithIndividualDistributionsPaid
/ us-gaap_PlanNameAxis
= ghm_LongTermIncentivePlanMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember
Employee Stock Purchase Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares authorized 200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
     
Stock based compensation expense 55us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
57us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
52us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
 
Income tax benefit to stock based compensation 19us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
20us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
19us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
 
Increase in capital in excess of par value for the income tax benefit realized upon exercise of stock options and vesting of restricted $ 3us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
$ 3us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
$ 2us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
 
Discounted purchase price of common stock percentage on fair market value 85.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
     
Issue of treasury stock to the ESPP for the offering periods 12,000ghm_SharesPurchasedByEmployeeStockPurchasePlan
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
16,000ghm_SharesPurchasedByEmployeeStockPurchasePlan
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember
19,000ghm_SharesPurchasedByEmployeeStockPurchasePlan
/ us-gaap_PlanNameAxis
= ghm_EmployeeStockPurchasePlanMember