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Note I - Components of Customer Sales Determined Based on the Location of Customers (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
UNITED STATES |  |  |
Revenues | $ 269,628 | $ 298,338 | $ 257,038
Revenues, Percent | 66.00% | 69.00% | 66.00%
Foreign Countries [Member] |  |  |
Revenues | $ 136,522 | $ 136,587 | $ 134,627
Revenues, Percent | 34.00% | 31.00% | 34.00%
Revenues | $ 406,150 | $ 434,925 | $ 391,665
Revenues, Percent | 100.00% | 100.00% | 100.00%

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- Definition The percentage of revenues by location. + References No definition available. + Details
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Namespace Prefix: | grc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_StatementGeographicalAxis=grc_ForeignCountriesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |