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Revenue Recognition - Schedule of Disaggregation of Revenue (Detail)	12 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Abstract]
Percentage of revenue from contracts recognized over time	80.00%	77.00%	74.00%
Percentage of revenue from contracts recognized upon shipment	20.00%	23.00%	26.00%

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

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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

X

- References

No definition available.

+ Details

Name:	us-gaap_DisaggregationOfRevenueAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration