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Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions | Mar. 26, 2021 | Dec. 25, 2020
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Statement of Financial Position [Abstract] |  |
Allowance for Credits | $ 5.0 | $ 4.4

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- Definition Allowance for Credits: Includes allowance for doubtful accounts and other credits against receivables. + References No definition available. + Details
Name: | ggg_AllowanceforCredits
Namespace Prefix: | ggg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_StatementOfFinancialPositionAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration