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Net Income per Common Share - Narrative (Details) - $ / shares shares in Millions | 6 Months Ended
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Jun. 30, 2018 | Jun. 30, 2017
Net Income per Common Share |  |
Stock options excluded from computation of diluted weighted average share outstanding | 3.0 | 2.8
Shares excluded from weighted average shares outstanding, exercise price | $ 11.65 | $ 9.42

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- Definition Average Share Price + References No definition available. + Details
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Namespace Prefix: | goro_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | na
Period Type: | duration