Significant Accounting Policies (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Deferred Lease Costs
Portion of compensation capitalized	$ 11.0	$ 9.6	$ 8.6
Estimated average lease term	7 years
Joint venture
Investment in Unconsolidated Joint Ventures
Amortization period of difference between carrying amount of investments and underlying equity in net assets	10 years
Recourse debt	$ 218.4
Number of joint ventures with debt recourse	2

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Represents the amount of deferred lease costs capitalized during the period.

+ References

No definition available.

+ Details

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- Definition

Represents the amortization period for the difference between the amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and the amount of underlying equity in net assets the reporting entity has in the investee.

+ References

No definition available.

+ Details

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- Definition

The number of joint ventures to whom the entity provides guarantees in the form of recourse for debt.

+ References

No definition available.

+ Details

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- Definition

Represents the estimated average term of the operating leases.

+ References

No definition available.

+ Details

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- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

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

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 45

-Paragraph 13

-Subparagraph 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

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