Annual report pursuant to Section 13 and 15(d)

The Company and Its Accounting Policies - Additional Information (Detail)

v2.4.1.9
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 $ 1,751,000us-gaap_ContractReceivableRetainage $ 901,000us-gaap_ContractReceivableRetainage    
Minimum level of likelihood 50.00%ghm_TestOfImpairmentMoreLikelihoodPercentage      
Research and development costs 3,585,000us-gaap_ResearchAndDevelopmentExpense 3,436,000us-gaap_ResearchAndDevelopmentExpense 3,579,000us-gaap_ResearchAndDevelopmentExpense  
Maximum stock authorized to purchase under stock repurchase program       18,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1
Antidilutive securities excluded from computation of earnings per share 12us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 2us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 14us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount  
Interest paid 11,000us-gaap_InterestPaidNet 12,000us-gaap_InterestPaidNet 59,000us-gaap_InterestPaidNet  
Income taxes paid 6,491,000us-gaap_IncomeTaxesPaid 3,302,000us-gaap_IncomeTaxesPaid 4,064,000us-gaap_IncomeTaxesPaid  
Pension and other postretirement benefit adjustments, net of tax 3,294,000us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax (2,275,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax (92,000)us-gaap_OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansAdjustmentNetOfTax  
Issuance of treasury stock 325,000us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued 317,000us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued 297,000us-gaap_StockIssuedDuringPeriodValueTreasuryStockReissued  
Capital expenditures 174,000us-gaap_CapitalExpendituresIncurredButNotYetPaid 40,000us-gaap_CapitalExpendituresIncurredButNotYetPaid 142,000us-gaap_CapitalExpendituresIncurredButNotYetPaid  
Capital leases $ 22,000us-gaap_CapitalLeaseObligationsIncurred $ 90,000us-gaap_CapitalLeaseObligationsIncurred $ 11,000us-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