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Exit Activity Costs And Asset Impairments (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2013 item | Dec. 31, 2012 item | Dec. 31, 2011 item
Exit Activity Costs And Asset Impairments [Abstract] |  |  |
Number of consolidated facilities | 2 | 2 | 3

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- Definition Number of consolidated facilities. + References No definition available. + Details
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Namespace Prefix: | rock_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RestructuringAndRelatedActivitiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration