Annual report pursuant to Section 13 and 15(d)

The Company and Its Accounting Policies - Summary of Costs and Estimated Earnings on Contracts (Detail)

v2.4.1.9
The Company and Its Accounting Policies - Summary of Costs and Estimated Earnings on Contracts (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Mar. 31, 2014
Accounting Policies [Abstract]    
Costs incurred since inception on contracts in progress $ 64,912ghm_CostOnContractInProgress $ 42,019ghm_CostOnContractInProgress
Estimated earnings since inception on contracts in progress 16,067ghm_EstimatedEarningsOnContractInProgress 10,208ghm_EstimatedEarningsOnContractInProgress
Costs and estimated earnings 80,979ghm_CostAndEstimatedEarningsOnContractInProgress 52,227ghm_CostAndEstimatedEarningsOnContractInProgress
Less billings to date 69,636ghm_BillingsToDate 57,489ghm_BillingsToDate
Net under (over) billings 11,343us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear  
Net under (over) billings   $ (5,262)us-gaap_BillingsInExcessOfCostCurrent