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v3.25.3

Revenue Recognition - Schedule of Disaggregation of Revenue (Detail) | 3 Months Ended | 6 Months Ended
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Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Disaggregation of Revenue [Abstract] |  |  |  |
Percentage of revenue from contracts recognized over time | 83.00% | 79.00% | 82.00% | 80.00%
Percentage of revenue from contracts recognized upon shipment | 17.00% | 21.00% | 18.00% | 20.00%

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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