Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Detail)

v2.4.1.9
Income Taxes - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Income Taxes [Line Items]    
Valuation allowance 952us-gaap_DeferredTaxAssetsValuationAllowance $ 738us-gaap_DeferredTaxAssetsValuationAllowance
Liability unrecognized tax benefits 0us-gaap_UnrecognizedTaxBenefits 0us-gaap_UnrecognizedTaxBenefits
Latest Tax Year [Member] | Federal Tax Jurisdictions [Member]    
Income Taxes [Line Items]    
Open tax year 2014  
Latest Tax Year [Member] | State Tax Jurisdictions [Member]    
Income Taxes [Line Items]    
Open tax year 2014  
Latest Tax Year [Member] | International Tax Jurisdictions [Member]    
Income Taxes [Line Items]    
Open tax year 2014  
Earliest Tax Year [Member] | Federal Tax Jurisdictions [Member]    
Income Taxes [Line Items]    
Open tax year 2013  
Earliest Tax Year [Member] | State Tax Jurisdictions [Member]    
Income Taxes [Line Items]    
Open tax year 2010  
Earliest Tax Year [Member] | International Tax Jurisdictions [Member]    
Income Taxes [Line Items]    
Open tax year 2012  
Investment Tax Credit Carryforward [Member]    
Income Taxes [Line Items]    
Deferred income taxes include the impact of state investment tax credits 344ghm_DeferredTaxAssetsTaxDeferredExpenseStateInvestmentTaxCreditsThatExpire
/ us-gaap_TaxCreditCarryforwardAxis
= us-gaap_InvestmentCreditMember
 
State investment tax credits with an unlimited carryforward period 608ghm_DeferredTaxAssetsTaxDeferredExpenseStateInvestmentTaxCreditsWithUnlimitedCarryforwardPeriod
/ us-gaap_TaxCreditCarryforwardAxis
= us-gaap_InvestmentCreditMember
 
Investment Tax Credit Carryforward [Member] | Minimum [Member]    
Income Taxes [Line Items]    
Expiration date of state investment tax credits Mar. 31, 2015  
Investment Tax Credit Carryforward [Member] | Maximum [Member]    
Income Taxes [Line Items]    
Expiration date of state investment tax credits Mar. 31, 2029