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Leases - Additional Information (Detail) | 6 Months Ended
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Sep. 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: |