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Related Party Transactions (Schedule of Related Party Legal Expense) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Related Party Transactions [Abstract]
Selling, general, and administrative expense	$ 1,357us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty	$ 1,763us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty	$ 1,511us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
Discontinued operations	0rock_RelatedPartyTransactionsExpensesFromDiscontinuedOperations	0rock_RelatedPartyTransactionsExpensesFromDiscontinuedOperations	12rock_RelatedPartyTransactionsExpensesFromDiscontinuedOperations
Capitalized as deferred financing costs	0rock_RelatedPartyTransactionsCapitalizedAsDeferredFinancingCosts	223rock_RelatedPartyTransactionsCapitalizedAsDeferredFinancingCosts	0rock_RelatedPartyTransactionsCapitalizedAsDeferredFinancingCosts
Total related-party legal costs	$ 1,357us-gaap_CostsAndExpensesRelatedParty	$ 1,986us-gaap_CostsAndExpensesRelatedParty	$ 1,523us-gaap_CostsAndExpensesRelatedParty

X

- Definition

Related Party Transactions Capitalized As Deferred Financing Costs

+ References

No definition available.

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Balance Type:	debit
Period Type:	duration

X

- Definition

Related party transactions, expenses from discontinued operations.

+ References

No definition available.

+ Details

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X

- Definition

Costs of sales and operating expenses for the period incurred from transactions with related parties.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.2)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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X

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 850

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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