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v3.23.1

Revenue Recognition - Schedule of Disaggregation of Revenue (Detail) | 12 Months Ended
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Mar. 31, 2023 | Mar. 31, 2022 | Mar. 31, 2021
Disaggregation of Revenue [Abstract] |  |  |
Percentage of revenue from contracts recognized over time | 74.00% | 75.00% | 60.00%
Percentage of revenue from contracts recognized upon shipment | 26.00% | 25.00% | 40.00%

X
- Definition The percentage of total revenue from contracts from customers from the satisfaction of performance obligations at a point in time. + References No definition available. + Details
Name: | ghm_PercentageOfRevenueFromContractsWithCustomersExcludingAssessedTaxPerformanceObligationSatisfiedAtPointInTime
Namespace Prefix: | ghm_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage of total revenue from contracts from customers from the satisfaction of performance obligations satisfied over time. + References No definition available. + Details
Name: | ghm_PercentageOfRevenueFromContractsWithCustomersExcludingAssessedTaxPerformanceObligationSatisfiedOverTime
Namespace Prefix: | ghm_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

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