Defined benefit plan effect on pension expense.

No definition available.

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

- Definition

Unrecognized Actuarial Gain (Loss) in Excess of Benefit Obligation, Percentage.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(7)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 45
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=123453770&loc=SL108413299-114919

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)(7)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Ultimate trend rate for health care cost for defined benefit postretirement plan.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

Name:	us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Details

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- Details

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- Details

Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DefinedBenefitPlanEquitySecuritiesMember
Namespace Prefix:
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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Note 9 - Pensions and Other Postretirement Benefits (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ 2,300	$ 4,600	$ 0
Unrecognized Actuarial Gain (Loss) in Excess of Benefit Obligation, Percentage	10.00%
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	$ 2,000
One Percentage Point Change in Assumed Rate of Return [Member]
Defined Benefit Plan Effect On Pension Expense	$ 700
One Percentage Point Increase in Discount Rate [Member]
Defined Benefit Plan Effect On Pension Expense		1,400
One Percentage Point Decrease in Discount Rate [Member]
Defined Benefit Plan Effect On Pension Expense			1,700
Defined Benefit Plan, Equity Securities [Member] \| Minimum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	22.00%
Defined Benefit Plan, Equity Securities [Member] \| Maximum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	42.00%
Fixed Income Securities [Member] \| Minimum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	50.00%
Fixed Income Securities [Member] \| Maximum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	70.00%
Alternative Investments [Member] \| Minimum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	3.00%
Alternative Investments [Member] \| Maximum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	13.00%
Defined Benefit Plan, Cash and Cash Equivalents [Member] \| Minimum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Defined Benefit Plan, Cash and Cash Equivalents [Member] \| Maximum [Member]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	10.00%
Pension Plan [Member]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 2,300	2,300	2,300
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement	$ (2,304)	$ (4,583)	$ (0)
Postretirement Health Coverage [Member]
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%