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Note 7 - Pension and Other Postretirement Benefits (Details Textual) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Defined Benefit Plan Effect On Pension Expense	$ 1.0	$ 4.4

X

- Definition

Defined benefit plan effect on pension expense.

+ References

No definition available.

+ Details

Name:	grc_DefinedBenefitPlanEffectOnPensionExpense
Namespace Prefix:	grc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration