XML 74 R62.htm IDEA: XBRL DOCUMENT
v3.19.1

Exit Activity Costs and Asset Impairments (Narrative) (Details) | 3 Months Ended
--- | ---
Mar. 31, 2018 facility
Restructuring and Related Activities [Abstract] |
Number of facilities closed | 1

X
- Definition Restructuring and Related Cost, Number of Facilities to be Closed + References No definition available. + Details
Name: | rock_RestructuringandRelatedCostNumberofFacilitiestobeClosed
Namespace Prefix: | rock_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_RestructuringAndRelatedActivitiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration