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Fair Value Measurements (Intangible Assets) (Details) | 12 Months Ended
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Dec. 31, 2013
Fair Value Inputs, Assets, Quantitative Information [Line Items] |
Discount rate (WACC) | 15.00%
Minimum [Member] |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |
Risk Premium | 1.00%
Royalty rate | 2.00%
Future attributable revenues | 77.00%
Maximum [Member] |
Fair Value Inputs, Assets, Quantitative Information [Line Items] |
Risk Premium | 1.00%
Royalty rate | 2.00%
Future attributable revenues | 97.00%

X
- Definition Rate of future attributable revenues, used as an input to measure fair value. + References No definition available. + Details
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Data Type: | num:percentItemType
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Period Type: | duration

X
- Definition Rate of return in excess of the risk-free rate of return that an investment is expected to yield, used as an input to measure fair value. + References No definition available. + Details
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Namespace Prefix: | rock_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Rate of payment to an owner for the use of property, used as an input to measure fair value. + References No definition available. + Details
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Namespace Prefix: | rock_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
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Period Type: | duration

X
- Definition Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258 + Details
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Balance Type: | na
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