Impairment Charges and Reserves - Summary of Significant Unobservable Inputs (Detail) - Fair Value Measurements [Member] $ in Millions	9 Months Ended
Sep. 30, 2017 USD ($) $ / a
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 141.0
Fair Value	327.3
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	141.0
Fair Value	327.3
Impairment of Consolidated Assets [Member] \| Level 3 [Member] \| Indicative Bid/Contracted Price [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	44.1
Impairment of Consolidated Assets [Member] \| Level 3 [Member] \| Income Capitalization/Sales Comparison Approach [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 74.7
Impairment of Consolidated Assets [Member] \| Level 3 [Member] \| Income Capitalization/Sales Comparison Approach [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	9.75%
Impairment of Consolidated Assets [Member] \| Level 3 [Member] \| Income Capitalization/Sales Comparison Approach [Member] \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	10.00%
Impairment of Consolidated Assets [Member] \| Level 3 [Member] \| Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 14.8
Range	9.00%
Range	10.00%
Impairment of Consolidated Assets [Member] \| Level 3 [Member] \| Sales Comparison Approach [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 7.4
Impairment of Consolidated Assets [Member] \| Level 3 [Member] \| Sales Comparison Approach [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Price per Acre, Range \| $ / a	50
Impairment of Consolidated Assets [Member] \| Level 3 [Member] \| Sales Comparison Approach [Member] \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Price per Acre, Range \| $ / a	218
Reserve of Preferred Equity Interests [Member] \| Level 3 [Member] \| Discounted Cash Flow [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 327.3
Range	1.00%
Reserve of Preferred Equity Interests [Member] \| Level 3 [Member] \| Discounted Cash Flow [Member] \| Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	8.20%
Range	4.60%
Reserve of Preferred Equity Interests [Member] \| Level 3 [Member] \| Discounted Cash Flow [Member] \| Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range	8.80%
Range	11.20%

Fair value inputs NOI growth rate.

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Fair value inputs rate price per acre.

+ References

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Fair value inputs terminal cap rate.

+ References

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Fair value of preferred equity interests.

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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=66048111&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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