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Note 7 - Pension and Other Postretirement Benefits (Details Textual) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Defined Benefit Plan Effect On Pension Expense	$ 1.9	$ 3.4

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- 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