Ebp, purchase limitations annual share maximum.

No definition available.

Name:	ghm_EBPPurchaseLimitationsAnnualShareMaximum
Namespace Prefix:	ghm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Ebp, purchase limitations shares aggregate fair market value limit maximum.

+ References

No definition available.

+ Details

Name:	ghm_EBPPurchaseLimitationsSharesAggregateFairMarketValueLimitMaximum
Namespace Prefix:	ghm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Ebp, purchase of shares limitations participant shares (as a percentage of total voting power).

+ References

No definition available.

+ Details

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

- Definition

Employee benefit plan investment number of shares reserved for future.

+ References

No definition available.

+ Details

Name:	ghm_EmployeeBenefitPlanInvestmentNumberOfSharesReservedForFuture
Namespace Prefix:	ghm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Employee benefit plan investment shares purchase price description.

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)
-SubTopic 205
-Topic 962
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478416/962-205-50-1

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanDescriptionOfPlanLineItems
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares or units of investment held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Employee Retirement Income Security Act of 1974
-Number 2520
-Section 103
-Subsection 6
-Paragraph d
-Subparagraph (1)(ii)
-Publisher DOL-EBSA

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Employee Retirement Income Security Act of 1974
-Number 2520
-Section 103
-Subsection 10
-Paragraph b
-Subparagraph (4)
-Publisher DOL-EBSA

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Employee Retirement Income Security Act of 1974
-Number 2520
-Section 103
-Subsection 10
-Paragraph b
-Subparagraph (3)
-Publisher DOL-EBSA

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Employee Retirement Income Security Act of 1974
-Number 2520
-Section 103
-Subsection 10
-Paragraph b
-Subparagraph (2)(i)(B)
-Publisher DOL-EBSA

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Employee Retirement Income Security Act of 1974
-Number 2520
-Section 103
-Subsection 10
-Paragraph b
-Subparagraph (1)(i)(B)
-Publisher DOL-EBSA

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-05(a)(Schedule I))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-02(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

+ Details

Name:	us-gaap-ebp_EmployeeBenefitPlanInvestmentNumberOfShares
Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares or units of investment purchased by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 962
-SubTopic 205
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6A-04(2)(b))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477804/962-205-S99-1

+ Details

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Namespace Prefix:	us-gaap-ebp_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=ghm_EBP001Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghm_OfferingPeriodAxis=ghm_AfterJuly12019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ghm_OfferingPeriodAxis=ghm_PriorToJuly12019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

The Plan - Additional Information (Detail) - EBP 001 [Member] - USD ($)	12 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024
EBP, Description of Plan [Line Items]
EBP, investment, purchased, number of shares	21,088	33,772	49,810
Employee benefit plan investment number of shares reserved for future	78,574
EPB, investment, number of shares	400,000
EBP, purchase of shares limitations participant shares as a percentage of total voting power	5.00%
EBP, purchase limitations shares aggregate fair market value limit maximum	$ 25,000
EBP, purchase limitations annual share maximum	5,000
After July 1, 2019 [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan investment shares purchase price description	85% of the lesser of the fair market value of the stock on the first or last business day of the six-month offering periods
Prior to July 1, 2019 [Member]
EBP, Description of Plan [Line Items]
Employee benefit plan investment shares purchase price description	95% of its fair market value on the first business day of the offering period