Impairment Charges and Impairment of Joint Venture Investments - Summary of Significant Unobservable Inputs (Detail) - Fair Value Measurements [Member] $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2015 USD ($) $ / ft²	Dec. 31, 2014 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 407.1	$ 141.2
Fair Value		6.4
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		$ 6.4
Impairment Of Consolidated Assets \| Income Capitalization/Sales Comparison Approach [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range		8.00%
Fair Value	$ 287.6	$ 67.0
Impairment Of Consolidated Assets \| Income Capitalization/Sales Comparison Approach [Member] \| Level 3 [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	8.00%
Price per Square Foot, Range \| $ / ft²	10.00
Impairment Of Consolidated Assets \| Income Capitalization/Sales Comparison Approach [Member] \| Level 3 [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	9.00%
Price per Square Foot, Range \| $ / ft²	40.00
Impairment Of Consolidated Assets \| Discounted Cash Flow [Member] \| Level 3 [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	10.00%
Range	8.00%
Impairment Of Consolidated Assets \| Discounted Cash Flow [Member] \| Level 3 [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	14.00%
Range	10.00%
Impairment Of Consolidated Assets \| Indicative Bid/Contracted Price [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 33.8	$ 74.2
Impairment Of Consolidated Assets \| Indicative Bid [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	51.5
Impairment Of Consolidated Assets \| Indicative Bid/Sales Comparison Approach [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	34.2
Impairment Of Joint Venture Investments \| Discounted Cash Flow [Member] \| Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range		15.00%
Range		6.00%
Fair Value	$ 0.0	$ 6.4

Fair value inputs rate per square foot.

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- Definition

Fair value inputs terminal cap rate.

+ References

No definition available.

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- Definition

Impaired equity method investments fair value disclosure.

+ References

No definition available.

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Fair value of long lived assets held and used and held for sale.

+ References

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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.

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- Definition

Ratio of the net operating income produced by an asset and its capital cost (original prices paid to buy the asset), used as an input to measure fair value.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bbb)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

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