Number of Significant Customers

No definition available.

Name:	rock_NumberofSignificantCustomers
Namespace Prefix:	rock_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Sale Leaseback Transaction, Annual Increase in Lease Payment

+ References

No definition available.

+ Details

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

- 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

- Details

Name:	rock_SignificantAccountingPoliciesLineItems
Namespace Prefix:	rock_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611

Reference 2: 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=6927468&loc=d3e6404-108592

Reference 3: 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=35750535&loc=d3e13531-108611

Reference 4: 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=6927468&loc=d3e6351-108592

+ 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 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

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_MinimumLeasePaymentsSaleLeasebackTransactionsWithinOneYear
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 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 deferred financing 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 51

-URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51840-112757

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 52

-URI http://asc.fasb.org/extlink&oid=28365400&loc=d3e51843-112757

+ Details

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

- Details

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

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
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:

Summary of Significant Accounting Policies (Narrative) (Details) (USD $)	1 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2014 customer	Dec. 31, 2013	Dec. 31, 2012
Significant Accounting Policies [Line Items]
Number of significant customers		2rock_NumberofSignificantCustomers
Advertising costs		$ 4,000,000us-gaap_AdvertisingExpense	$ 4,000,000us-gaap_AdvertisingExpense	$ 3,600,000us-gaap_AdvertisingExpense
Sale price	4,500,000
Percent leased back	50.00%
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
Annual increase in lease payment	3.00%
Period of lease payment increase	4 years
Minimum \| Land, Buildings and Improvements
Significant Accounting Policies [Line Items]
Estimated useful lives		15 years
Minimum \| Machinery and Equipment
Significant Accounting Policies [Line Items]
Estimated useful lives		3 years
Maximum \| Land, Buildings and Improvements
Significant Accounting Policies [Line Items]
Estimated useful lives		40 years
Maximum \| Machinery and Equipment
Significant Accounting Policies [Line Items]
Estimated useful lives		20 years
Residential Products \| Home Improvement Retail Company \| Accounts Receivable
Significant Accounting Policies [Line Items]
Concentrations of credit risk		17.10%	11.50%
Residential Products \| Home Improvement Retail Company \| Net sales
Significant Accounting Policies [Line Items]
Concentrations of credit risk		11.50%	12.30%
Residential Products \| Foreign Postal Operator \| Accounts Receivable
Significant Accounting Policies [Line Items]
Concentrations of credit risk		11.50%	3.00%