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Revenue Recognition - Schedule of Disaggregation of Revenue (Detail) | 3 Months Ended | 9 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2024 | Dec. 31, 2023
Disaggregation of Revenue [Abstract] |  |  |  |
Percentage of revenue from contracts recognized over time | 75.00% | 76.00% | 79.00% | 77.00%
Percentage of revenue from contracts recognized upon shipment | 25.00% | 24.00% | 21.00% | 23.00%

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- 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

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- 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