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

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- Definition

Maximum number of shares originally approved, net of subsequent amendments and adjustments, for awards of Incentive Stock Options under the equity-based compensation plan.

+ Details

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Period Type:	duration

- Definition

Number Of Restricted Stock Units Credited To Participant Account

+ Details

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Namespace Prefix:	rock
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Performance stock units earned during the first two performance periods.

+ Details

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Balance Type:	na
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- Definition

Compensation expense recognized for surrendered restricted stock unit award.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Targeted performance stock units for the first two performance periods.

+ Details

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph b(2)(c)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph c(1)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-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=6415400&loc=d3e5070-113901

+ Details

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Period Type:	duration

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph b(2)(a)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph b(2)(b)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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Data Type:	xbrli:sharesItemType
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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

+ References

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:sharesItemType
Balance Type:	na
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Equity-Based Compensation (Narrative) (Details) (USD $)	6 Months Ended	12 Months Ended	6 Months Ended		12 Months Ended			6 Months Ended		12 Months Ended	6 Months Ended	12 Months Ended
Equity-Based Compensation (Narrative) (Details) (USD $)	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 2005 Equity Incentive Plan [Member]	Jun. 30, 2011 Performance Stock Units [Member]	Dec. 31, 2010 Performance Stock Units [Member]	Dec. 31, 2009 Performance Stock Units [Member]	Sep. 30, 2009 Performance Stock Units [Member]	Jun. 30, 2011 Management Stock Purchase Plan [Member]	Jun. 30, 2010 Management Stock Purchase Plan [Member]	Dec. 31, 2010 Management Stock Purchase Plan [Member]	Jun. 30, 2011 Unvested Restricted Stock Unit [Member]	Dec. 31, 2010 Unvested Restricted Stock Unit [Member]
Maximum number of shares that may be issued under the Plan			3,000,000
Maximum number of shares that may be issued in connection with grants of incentive stock options and rights			900,000
Unamortized portion of compensation expense related to awards	$ 885,000
Percentage of target performance stock units earned					0.00%	34.00%
Targeted performance stock units for the first two performance periods				589,834
Performance stock units earned during the first two performance periods				100,300
Performance stock units outstanding				868,000			905,000
Weighted average fair value of per unit awarded				$ 4.31	$ 7.92			$ 11.18		$ 11.03
Number of restricted stock units credited to participant accounts	523,468	457,343						154,507	143,870		64,581	84,635