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Accumulated Other Comprehensive (Loss) Income (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] |  |  |
Balance at begging of period | $ (4,381)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 | $ (2,429)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 |
Other comprehensive loss on cash flow hedge before reclassification | (875)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax |  |
Reclassified loss on cash flow hedge from other comprehensive (loss) income | 650 us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax |  |
Balance at end of period | (11,268)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 | (4,381)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 | (2,429)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
Tax (Benefit) Expense |  |  |
Balance at beginning of period | (796)rock_AccumulatedOtherComprehensiveIncomeLossTax | (854)rock_AccumulatedOtherComprehensiveIncomeLossTax |
Other comprehensive loss on cash flow hedge before reclassification | (319)rock_OtherComprehensiveIncomeLossbeforeReclassificationsTax |  |
Reclassified loss on cash flow hedge from other comprehensive (loss) income | 237 rock_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax |  |
Minimum pension and post retirement health care plan adjustments | (839)us-gaap_OtherComprehensiveIncomeLossTax | 58 us-gaap_OtherComprehensiveIncomeLossTax |
Balance at end of period | (1,717)rock_AccumulatedOtherComprehensiveIncomeLossTax | (796)rock_AccumulatedOtherComprehensiveIncomeLossTax | (854)rock_AccumulatedOtherComprehensiveIncomeLossTax
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Balance at beginning of period | (3,585)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax | (1,575)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax |
Other comprehensive loss on cash flow hedge before reclassification | (556)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax |  |
Reclassified loss on cash flow hedge from other comprehensive (loss) income | 413 us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax |  |
Other Comprehensive Income (Loss), Net of Tax | (5,966)us-gaap_OtherComprehensiveIncomeLossNetOfTax | (2,010)us-gaap_OtherComprehensiveIncomeLossNetOfTax | 1,775 us-gaap_OtherComprehensiveIncomeLossNetOfTax
Balance at end of period | (9,551)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax | (3,585)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax | (1,575)us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax
Foreign Currency Translation Adjustment |  |  |
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] |  |  |
Balance at begging of period | (2,201)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedTranslationAdjustmentMember | (93)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedTranslationAdjustmentMember |
Other Comprehensive Income (Loss), before Tax | (4,364)us-gaap_OtherComprehensiveIncomeLossBeforeTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedTranslationAdjustmentMember | (2,108)us-gaap_OtherComprehensiveIncomeLossBeforeTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedTranslationAdjustmentMember |
Balance at end of period | (6,565)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedTranslationAdjustmentMember | (2,201)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedTranslationAdjustmentMember |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Other Comprehensive Income (Loss), Net of Tax | (4,364)us-gaap_OtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedTranslationAdjustmentMember | (2,108)us-gaap_OtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedTranslationAdjustmentMember |
Cash Flow Hedges |  |  |
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] |  |  |
Balance at begging of period | 0 us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  |
Other comprehensive loss on cash flow hedge before reclassification | (875)us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  |
Reclassified loss on cash flow hedge from other comprehensive (loss) income | 650 us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  |
Balance at end of period | (225)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  | 0 us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Unrealized loss on cash flow hedges expected to be reclassified into earnings within twelve months | 225 us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetGainLossFromDesignatedOrQualifyingCashFlowHedgesMember |  |
Accumulated Defined Benefit Plans Adjustment |  |  |
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] |  |  |
Other Comprehensive Income (Loss), before Tax | (2,298)us-gaap_OtherComprehensiveIncomeLossBeforeTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | 156 us-gaap_OtherComprehensiveIncomeLossBeforeTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Other Comprehensive Income (Loss), Net of Tax | (1,459)us-gaap_OtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | 98 us-gaap_OtherComprehensiveIncomeLossNetOfTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
Accumulated Defined Benefit Plans Adjustment | Minimum Pension Liability Adjustment |  |  |
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] |  |  |
Balance at begging of period | 76 us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (8)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
Other Comprehensive Income (Loss), before Tax | (33)us-gaap_OtherComprehensiveIncomeLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | 84 us-gaap_OtherComprehensiveIncomeLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
Balance at end of period | 43 us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | 76 us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_PensionPlansDefinedBenefitMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
Accumulated Defined Benefit Plans Adjustment | Unamortized Post-Retirement Health Care Costs |  |  |
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward] |  |  |
Balance at begging of period | (2,256)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | (2,328)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
Other Comprehensive Income (Loss), before Tax | (2,265)us-gaap_OtherComprehensiveIncomeLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | 72 us-gaap_OtherComprehensiveIncomeLossBeforeTax / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |
Balance at end of period | $ (4,521)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember | $ (2,256)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = us-gaap_DefinedBenefitPostretirementHealthCoverageMember / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember |

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- Definition Other Comprehensive Income (Loss), before Reclassifications, Tax + References No definition available. + Details
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- Definition Amount before tax of increase (decrease) in accumulated in equity from transactions and other events and circumstances from non-owner sources. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners). + References No definition available. + Details
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- Definition Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e681-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 31 -Article 5 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 + Details
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- Definition The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994 + Details
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- Definition Amount before tax, after reclassification adjustments of other comprehensive income (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669619-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669625-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33775-111570 + Details
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