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Revenue Recognition - Additional Information (Detail) - USD ($) $ in Thousands | Sep. 30, 2025 | Mar. 31, 2025
--- | --- | ---
Contract With Customer Assets And Liabilities [Line Items] |  |
Receivables billed but not paid under retainage provisions in its customer contracts | $ 1,563 | $ 1,999
Revenue remaining unsatisfied performance obligations amount | 500,072 |
Customer Deposit [Member] |  |
Contract With Customer Assets And Liabilities [Line Items] |  |
Contract liabilities | $ 10,948 | $ 12,315

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- Definition Contract with customer assets and liabilities. + References No definition available. + Details
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Namespace Prefix: | ghm_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The amount of obligation to transfer good or service to customer for which consideration is receivable. + References No definition available. + Details
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Namespace Prefix: | ghm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount billed to customers under long-term contracts or programs that have been withheld because of retainage provisions in a contract. + References No definition available. + Details
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Namespace Prefix: | ghm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition Amount of transaction price allocated to performance obligation that has not been recognized as revenue. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 13 -Subparagraph (a) -SubTopic 10 -Topic 606 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479806/606-10-50-13 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |