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Leases - Additional Information (Detail)	3 Months Ended
	Jun. 30, 2021
Leases [Line Items]
Lessee, option to renew or terminate leases, description	Certain leases include options to renew or terminate.  Renewal options are exercisable per the discretion of the Company and vary based on the nature of each lease.
Minimum [Member]
Leases [Line Items]
Remaining term of contract	1 year
Maximum [Member]
Leases [Line Items]
Remaining term of contract	5 years

X

- Definition

Leases.

+ References

No definition available.

+ Details

Name:	ghm_LeasesLineItems
Namespace Prefix:	ghm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Lessee operating and finance lease remaining term of contract.

+ References

No definition available.

+ Details

Name:	ghm_LesseeOperatingAndFinanceLeaseRemainingTermOfContract
Namespace Prefix:	ghm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Lessee operating lease and finance lease option to renew or terminate.

+ References

No definition available.

+ Details

Name:	ghm_LesseeOperatingLeaseAndFinanceLeaseOptionToRenewOrTerminate
Namespace Prefix:	ghm_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: