Minimum Lease Payments, Sale Leaseback Transactions, Escalation Rate

No definition available.

Name:	rock_MinimumLeasePaymentsSaleLeasebackTransactionsEscalationRate
Namespace Prefix:	rock_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Revenue Recognition, Revenue Recognized Under Percentage-of-Completion Method

+ References

No definition available.

+ Details

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

- Definition

Sale Leaseback Transaction, Percent Leased after Transaction

+ References

No definition available.

+ Details

Name:	rock_SaleLeasebackTransactionPercentLeasedafterTransaction
Namespace Prefix:	rock_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Sale Leaseback Transaction, Period of Lease

+ References

No definition available.

+ Details

Name:	rock_SaleLeasebackTransactionPeriodofLease
Namespace Prefix:	rock_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Sale Leaseback Transaction, Period of Lease Payment Increase

+ References

No definition available.

+ Details

Name:	rock_SaleLeasebackTransactionPeriodofLeasePaymentIncrease
Namespace Prefix:	rock_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Sale Leaseback Transaction, Portion of Gain Above Fair Value of Minimum Lease Payments

+ References

No definition available.

+ Details

Name:	rock_SaleLeasebackTransactionPortionofGainAboveFairValueofMinimumLeasePayments
Namespace Prefix:	rock_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 720
-SubTopic 35
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848

+ Details

Name:	us-gaap_AdvertisingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of minimum lease payments for sale-leaseback transactions accounted for using the deposit method or as a financing due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6456377&loc=d3e50824-112756

+ Details

Name:	us-gaap_MinimumLeasePaymentsSaleLeasebackTransactionsWithinFiveYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of minimum lease payments for sale-leaseback transactions accounted for using the deposit method or as a financing due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_MinimumLeasePaymentsSaleLeasebackTransactionsWithinFourYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of minimum lease payments for sale-leaseback transactions accounted for using the deposit method or as a financing due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_MinimumLeasePaymentsSaleLeasebackTransactionsWithinOneYear
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of minimum lease payments for sale-leaseback transactions accounted for using the deposit method or as a financing due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_MinimumLeasePaymentsSaleLeasebackTransactionsWithinThreeYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of minimum lease payments for sale-leaseback transactions accounted for using the deposit method or as a financing due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_MinimumLeasePaymentsSaleLeasebackTransactionsWithinTwoYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of minimum lease payments for sale-leaseback transactions accounted for using the deposit method or as a financing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737

+ Details

Name:	us-gaap_PresentValueOfFutureMinimumLeasePaymentsSaleLeasebackTransactions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

+ Details

Name:	us-gaap_ResearchAndDevelopmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of the gain recorded in connection with the transaction involving the sale of property to another party and the lease of the property back to the seller to be recognized in future periods.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 25
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6456126&loc=d3e49567-112750

+ Details

Name:	us-gaap_SaleLeasebackTransactionDeferredGainGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of cash inflow before closing and debt issuance costs received by a seller-lessee in a sale-leaseback recognized in investing activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 55
-Paragraph 52
-URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51843-112757

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 55
-Paragraph 50
-URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51831-112757

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 55
-Paragraph 51
-URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51840-112757

+ Details

Name:	us-gaap_SaleLeasebackTransactionGrossProceedsInvestingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Details

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

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LandBuildingsAndImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_MachineryAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=rock_ResidentialProductsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorCustomersAxis=rock_HomeImprovementRetailCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AccountsReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MajorCustomersAxis=rock_ForeignPostalOperatorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SaleLeasebackTransactionDescriptionAxis=rock_RealEstatePropertySaleLeasebackFirstQuarterTwoThousandFifteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SaleLeasebackTransactionDescriptionAxis=rock_RealEstatePropertySaleLeasebackJuneTwoThousandFourteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2014	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2015
Sale Leaseback Transaction [Line Items]
Revenue recognized under the percentage-of-completion method			25.80%	16.70%
Advertising costs			$ 5,100,000	$ 4,700,000	$ 4,000,000
Research and development cost			$ 2,200,000	$ 866,000	$ 60,000
Minimum \| Land, Buildings and Improvements
Sale Leaseback Transaction [Line Items]
Estimated useful lives			15 years
Minimum \| Machinery and Equipment
Sale Leaseback Transaction [Line Items]
Estimated useful lives			3 years
Maximum \| Land, Buildings and Improvements
Sale Leaseback Transaction [Line Items]
Estimated useful lives			40 years
Maximum \| Machinery and Equipment
Sale Leaseback Transaction [Line Items]
Estimated useful lives			20 years
Residential Products \| Home Improvement Retail Company \| Accounts Receivable
Sale Leaseback Transaction [Line Items]
Concentrations of credit risk			13.70%	11.80%
Residential Products \| Home Improvement Retail Company \| Net sales
Sale Leaseback Transaction [Line Items]
Concentrations of credit risk			11.40%	10.60%	12.00%
Residential Products \| Postal Authority \| Accounts Receivable
Sale Leaseback Transaction [Line Items]
Concentrations of credit risk				5.50%
First quarter 2015 Sale Leaseback
Sale Leaseback Transaction [Line Items]
Sale price		$ 26,373,000
Period of lease		5 years
Net present value of future minimum lease payments						$ 5,765,000
Deferred gain on sale						13,144,000
Gain above minimum lease payments fair value						7,379,000
Minimum lease payment for first year						1,378,000,000
Minimum lease payments year 2						1,378,000,000
Minimum lease payments year 3						1,378,000,000
Minimum lease payments year 4						1,378,000,000
Minimum lease payments year 5						$ 1,378,000,000
June 2014 Sale Leaseback
Sale Leaseback Transaction [Line Items]
Sale price	$ 4,500,000
Period of lease	5 years
Net present value of future minimum lease payments	$ 892,000
Deferred gain on sale	829,000
Minimum lease payment for first year	$ 202,000
Percent leased back	50.00%
Lease payment escalation rate	3.00%
Period of lease payment increase	4 years