XML 59 R48.htm IDEA: XBRL DOCUMENT
v3.22.1

Equity-Based Compensation (Incentive Plan) (Details) - Common Stock - shares | May 04, 2018 | Dec. 31, 2016
--- | --- | ---
2018 Plan |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of shares authorized (in shares) | 1,000,000 |
Non-Employee Directors Plan |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of shares authorized (in shares) |  | 100,000

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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of shares authorized for issuance under share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_PlanNameAxis=rock_A2018PlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_CommonStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_PlanNameAxis=rock_NonEmployeeDirectorsPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |