XML 113 R90.htm IDEA: XBRL DOCUMENT v3.10.0.1

Equity-Based Compensation (PSUs Eligible for Conversion to Cash) (Details) - Performance stock units - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units (in shares)		128,000
Grant date fair value		$ 3,100
Percent of targeted performance stock units earned	200.00%
Units vested (in shares)	256,000

X

- Definition

Percentage of performance stock units earned during performance period based on the terms of the performance stock unit award.

+ References

No definition available.

+ Details

Name:	rock_EquityBasedCompensationPercentOfTargetedPerformanceStockUnitsEarned
Namespace Prefix:	rock_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Units Earned and Convertible to Cash

+ References

No definition available.

+ Details

Name:	rock_SharebasedCompensationArrangementbySharebasedPaymentAwardEquityInstrumentsOtherthanOptionsUnitsEarnedandConvertibletoCash
Namespace Prefix:	rock_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

+ 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 (d)(2)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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 options vested.

+ References

No definition available.

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedNumberOfShares
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: