Revenue Recognition - Schedule of Disaggregation of Revenue (Detail)	3 Months Ended
Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Abstract]
Percentage of revenue from contracts recognized over time	82.00%	81.00%
Percentage of revenue from contracts recognized upon shipment	18.00%	19.00%

The percentage of total revenue from contracts from customers from the satisfaction of performance obligations at a point in time.

No definition available.

Name:	ghm_PercentageOfRevenueFromContractsWithCustomersExcludingAssessedTaxPerformanceObligationSatisfiedAtPointInTime
Namespace Prefix:	ghm_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration