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Revenue Recognition - Schedule of Disaggregation of Revenue (Detail)	3 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Disaggregation of Revenue [Abstract]
Percentage of revenue from contracts recognized over time	81.00%	65.00%
Percentage of revenue from contracts recognized upon shipment	19.00%	35.00%

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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

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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

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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