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Goodwill And Related Intangible Assets (Schedule Of Goodwill Impairment Tests) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Maximum [Member]	Oct. 31, 2013 Maximum [Member]	Oct. 31, 2012 Maximum [Member]	Dec. 31, 2013 Minimum [Member]	Oct. 31, 2013 Minimum [Member]	Oct. 31, 2012 Minimum [Member]
Goodwill [Line Items]
Date of impairment test	Oct. 31, 2013	Oct. 31, 2012
WACC			13.40%	12.70%	13.10%	12.90%	11.10%	10.70%

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- Definition

Weighted Average Cost Of Capital

+ References

No definition available.

+ Details

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Namespace Prefix:	rock_
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Balance Type:	na
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X

- Definition

Weighted average cost of capital used to discount cash flows in the annual goodwill impairment test.

+ References

No definition available.

+ Details

Name:	rock_WeightedAverageCostOfCapitalDateOfAnnualImpairmentTest
Namespace Prefix:	rock_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

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- Details

Name:	us-gaap_GoodwillLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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Period Type:	duration