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Summary of Significant Accounting Policies (Narrative) (Details) (USD $) | 1 Months Ended | 12 Months Ended
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Jun. 30, 2014 | Dec. 31, 2014 customer | Dec. 31, 2013 | Dec. 31, 2012
Significant Accounting Policies [Line Items] |  |  |  |
Number of significant customers |  | 2 rock_NumberofSignificantCustomers |  |
Advertising costs |  | $ 4,000,000 us-gaap_AdvertisingExpense | $ 4,000,000 us-gaap_AdvertisingExpense | $ 3,600,000 us-gaap_AdvertisingExpense
Sale price | 4,500,000 us-gaap_SaleLeasebackTransactionGrossProceedsInvestingActivities |  |  |
Percent leased back | 50.00%rock_SaleLeasebackTransactionPercentLeasedafterTransaction |  |  |
Period of lease | 5 years |  |  |
Net present value of future minimum lease payments | 892,000 us-gaap_PresentValueOfFutureMinimumLeasePaymentsSaleLeasebackTransactions |  |  |
Deferred gain on sale | 829,000 us-gaap_SaleLeasebackTransactionDeferredGainGross |  |  |
Minimum lease payment for first year | $ 202,000 us-gaap_MinimumLeasePaymentsSaleLeasebackTransactionsWithinOneYear |  |  |
Annual increase in lease payment | 3.00%rock_SaleLeasebackTransactionAnnualIncreaseinLeasePayment |  |  |
Period of lease payment increase | 4 years |  |  |
Minimum | Land, Buildings and Improvements |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Estimated useful lives |  | 15 years |  |
Minimum | Machinery and Equipment |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Estimated useful lives |  | 3 years |  |
Maximum | Land, Buildings and Improvements |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Estimated useful lives |  | 40 years |  |
Maximum | Machinery and Equipment |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Estimated useful lives |  | 20 years |  |
Residential Products | Home Improvement Retail Company | Accounts Receivable |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Concentrations of credit risk |  | 17.10%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_MajorCustomersAxis = rock_HomeImprovementRetailCompanyMember / us-gaap_StatementBusinessSegmentsAxis = rock_ResidentialProductsMember | 11.50%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_MajorCustomersAxis = rock_HomeImprovementRetailCompanyMember / us-gaap_StatementBusinessSegmentsAxis = rock_ResidentialProductsMember |
Residential Products | Home Improvement Retail Company | Net sales |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Concentrations of credit risk |  | 11.50%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_MajorCustomersAxis = rock_HomeImprovementRetailCompanyMember / us-gaap_StatementBusinessSegmentsAxis = rock_ResidentialProductsMember | 12.30%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_MajorCustomersAxis = rock_HomeImprovementRetailCompanyMember / us-gaap_StatementBusinessSegmentsAxis = rock_ResidentialProductsMember |
Residential Products | Foreign Postal Operator | Accounts Receivable |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |
Concentrations of credit risk |  | 11.50%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_MajorCustomersAxis = rock_ForeignPostalOperatorMember / us-gaap_StatementBusinessSegmentsAxis = rock_ResidentialProductsMember | 3.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_AccountsReceivableMember / us-gaap_MajorCustomersAxis = rock_ForeignPostalOperatorMember / us-gaap_StatementBusinessSegmentsAxis = rock_ResidentialProductsMember |

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- Definition Sale Leaseback Transaction, Annual Increase in Lease Payment + References No definition available. + Details
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- Definition Sale Leaseback Transaction, Percent Leased after Transaction + References No definition available. + Details
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- Definition Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 720 -SubTopic 35 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848 + Details
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- Definition For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 21 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 275 -SubTopic 10 -Section 50 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592 + Details
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- Definition Amount of minimum lease payments for sale-leaseback transactions accounted for using the deposit method or as a financing due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 40 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6456377&loc=d3e50824-112756 + Details
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- Definition Present value of minimum lease payments for sale-leaseback transactions accounted for using the deposit method or as a financing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737 + Details
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- Definition Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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- Definition The amount of the gain recorded in connection with the transaction involving the sale of property to another party and the lease of the property back to the seller to be recognized in future periods. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 40 -Section 25 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6456126&loc=d3e49567-112750 + Details
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- Definition Amount of cash inflow before closing and deferred financing costs received by a seller-lessee in a sale-leaseback recognized in investing activities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 40 -Section 55 -Paragraph 51 -URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51840-112757 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 40 -Section 55 -Paragraph 50 -URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51831-112757 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 40 -Section 55 -Paragraph 52 -URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51843-112757 + Details
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