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Note 7 - Pensions and Other Postretirement Benefits (Details Textual) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
One Percentage Point Decrease in Discount Rate [Member]
Defined Benefit Plan Effect On Pension Expense	$ 1.5

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

X

- Details

Name:	srt_StatementScenarioAxis=grc_OnePercentagePointDecreaseInDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: