XML 82 R64.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Goodwill and Related Intangible Assets (Schedule of Acquired Intangible Assets) (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount, Finite-lived intangible assets | $ 116,339 | $ 113,646
Total acquired intangible assets, Gross Carrying Amount | 161,446 | 158,366
Accumulated Amortization, Finite-lived intangible assets | 55,678 | 47,576
Total acquired intangible assets, Accumulated Amortization | 55,678 | 47,576
Trademarks |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount, Finite-lived intangible assets | 5,876 | 5,808
Accumulated Amortization, Finite-lived intangible assets | 3,062 | 2,427
Unpatented technology and patents |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount, Finite-lived intangible assets | 28,107 | 26,720
Accumulated Amortization, Finite-lived intangible assets | 12,033 | 10,041
Customer relationships |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount, Finite-lived intangible assets | 80,707 | 78,569
Accumulated Amortization, Finite-lived intangible assets | 39,652 | 33,585
Non-compete agreements |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount, Finite-lived intangible assets | 1,649 | 1,649
Accumulated Amortization, Finite-lived intangible assets | 931 | 623
Backlog |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount, Finite-lived intangible assets | 0 | 900
Accumulated Amortization, Finite-lived intangible assets | 0 | 900
Trademarks |  |
Finite-Lived Intangible Assets [Line Items] |  |
Gross Carrying Amount, Indefinite-lived intangible assets | 45,107 | 44,720
Accumulated Amortization, Indefinite-lived intangible assets | $ 0 | $ 0
Minimum | Trademarks |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 5 years |
Minimum | Unpatented technology and patents |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 5 years |
Minimum | Customer relationships |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 5 years |
Minimum | Non-compete agreements |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 4 years |
Minimum | Backlog |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 6 months |
Maximum | Trademarks |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 15 years |
Maximum | Unpatented technology and patents |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 20 years |
Maximum | Customer relationships |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 17 years |
Maximum | Non-compete agreements |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 10 years |
Maximum | Backlog |  |
Finite-Lived Intangible Assets [Line Items] |  |
Estimated Useful Life | 2 years |

X
- Definition Acquired Intangible Assets, Total. + References No definition available. + Details
Name: | rock_AcquiredIntangibleAssetsTotal
Namespace Prefix: | rock_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Indefinite-lived accumulated amortization. + References No definition available. + Details
Name: | rock_IndefiniteLivedAccumulatedAmortization
Namespace Prefix: | rock_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Total acquired intangible assets, accumulated amortization + References No definition available. + Details
Name: | rock_TotalAcquiredIntangibleAssetsAccumulatedAmortization
Namespace Prefix: | rock_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FiniteLivedIntangibleAssetsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
Name: | us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TrademarksMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_UnpatentedTechnologyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_CustomerRelationshipsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_NoncompeteAgreementsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_OrderOrProductionBacklogMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_TrademarksMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |