XML 70 R58.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Equity-Based Compensation (Equity Based Awards - Settled in Stock) (Details) - Performance stock units - shares | 1 Months Ended | 9 Months Ended
--- | --- | ---
Feb. 29, 2020 | Apr. 30, 2017 | Feb. 28, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Units awarded (in shares) |  |  |  | 135,540 | 108,748
Performance period |  |  |  | 1 year |
2015 Incentive Plan |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Units awarded that will convert to shares (in shares) |  |  | 78,482 |  |
Shares to be issued on conversion as percentage of total award |  |  | 30.00% |  |
Units awarded (in shares) |  | 10,266 | 20,000 |  |
Performance period |  |  | 3 years |  |
Scenario, Forecast | 2015 Incentive Plan |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |
Shares to be issued on conversion (in shares) | 23,546 |  |  |  |

X
- Definition Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Grants In Period Expected To Convert, Percentage Of Total Award + References No definition available. + Details
Name: | rock_SharebasedCompensationArrangementBySharebasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodExpectedToConvertPercentageOfTotalAward
Namespace Prefix: | rock_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Award Performance Period + References No definition available. + Details
Name: | rock_SharebasedCompensationArrangementbySharebasedPaymentAwardAwardPerformancePeriod
Namespace Prefix: | rock_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Expected to Convert + References No definition available. + Details
Name: | rock_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsGrantsinPeriodExpectedtoConvert
Namespace Prefix: | rock_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + 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 (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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 issued during the period as a result of the conversion of convertible securities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29-30) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644 + Details
Name: | us-gaap_StockIssuedDuringPeriodSharesConversionOfConvertibleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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

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

X
- Details
Name: | us-gaap_StatementScenarioAxis=us-gaap_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |