Annual report pursuant to Section 13 and 15(d)

Schedule II - Valuation and Qualifying Accounts (Detail)

v2.4.1.9
Schedule II - Valuation and Qualifying Accounts (Detail) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2013
Reserve for Doubtful Accounts Receivable [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Period $ 46us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
$ 33us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
$ 43us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
Charged to Costs and Expenses 24us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
19us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
(10)us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
Charged to Other Accounts 0us-gaap_ValuationAllowancesAndReservesChargedToOtherAccounts
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
0us-gaap_ValuationAllowancesAndReservesChargedToOtherAccounts
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
0us-gaap_ValuationAllowancesAndReservesChargedToOtherAccounts
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
Deductions (8)us-gaap_ValuationAllowancesAndReservesDeductions
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
(6)us-gaap_ValuationAllowancesAndReservesDeductions
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
 
Balance at End of Period 62us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
46us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
33us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_AllowanceForDoubtfulAccountsMember
Product Warranty Liability [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Balance at Beginning of Period 308us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
408us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
215us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
Charged to Costs and Expenses 930us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
125us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
360us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
Charged to Other Accounts 0us-gaap_ValuationAllowancesAndReservesChargedToOtherAccounts
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
0us-gaap_ValuationAllowancesAndReservesChargedToOtherAccounts
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
0us-gaap_ValuationAllowancesAndReservesChargedToOtherAccounts
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
Deductions (585)us-gaap_ValuationAllowancesAndReservesDeductions
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
(225)us-gaap_ValuationAllowancesAndReservesDeductions
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
(167)us-gaap_ValuationAllowancesAndReservesDeductions
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
Balance at End of Period 653us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
308us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
408us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= us-gaap_WarrantyReservesMember
Restructuring Reserve [Member]      
Valuation and Qualifying Accounts Disclosure [Line Items]      
Charged to Costs and Expenses 1,718us-gaap_ValuationAllowancesAndReservesChargedToCostAndExpense
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= ghm_RestructuringReserveMember
   
Charged to Other Accounts 0us-gaap_ValuationAllowancesAndReservesChargedToOtherAccounts
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= ghm_RestructuringReserveMember
   
Balance at End of Period $ 1,718us-gaap_ValuationAllowancesAndReservesBalance
/ us-gaap_ValuationAllowancesAndReservesTypeAxis
= ghm_RestructuringReserveMember