Quarterly report pursuant to Section 13 or 15(d)

Product Warranty Liability - Reconciliation of the Changes in Product Warranty Liability (Detail)

v2.4.1.9
Product Warranty Liability - Reconciliation of the Changes in Product Warranty Liability (Detail) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 9 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Guarantees [Abstract]        
Balance at beginning of period $ 347us-gaap_ProductWarrantyAccrual $ 299us-gaap_ProductWarrantyAccrual $ 308us-gaap_ProductWarrantyAccrual $ 408us-gaap_ProductWarrantyAccrual
Expense for product warranties 436ghm_ProductWarrantyIncomeExpense (47)ghm_ProductWarrantyIncomeExpense 573ghm_ProductWarrantyIncomeExpense 11ghm_ProductWarrantyIncomeExpense
Product warranty claims paid (63)us-gaap_StandardProductWarrantyAccrualPayments (29)us-gaap_StandardProductWarrantyAccrualPayments (161)us-gaap_StandardProductWarrantyAccrualPayments (196)us-gaap_StandardProductWarrantyAccrualPayments
Balance at end of period $ 720us-gaap_ProductWarrantyAccrual $ 223us-gaap_ProductWarrantyAccrual $ 720us-gaap_ProductWarrantyAccrual $ 223us-gaap_ProductWarrantyAccrual