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Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Mar. 31, 2023 | Mar. 31, 2022 | Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract] |  |  |
Virgin Orbit reserves | $ 3,050 | $ 0 | $ 0

X
- Definition Reserves for the Virgin Orbit bankruptcy. + References No definition available. + Details
Name: | ghm_VirginOrbitReserves
Namespace Prefix: | ghm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration