Impairment Charges and Impairment of Joint Venture Investments - Summary of Significant Unobservable Inputs (Detail) (Level 3 [Member], Fair Value Measurements [Member], USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Impairment of Consolidated Assets [Member] | Income Capitalization Approach [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	$ 67.0	$ 75.5
Valuation Technique	Income Capitalization Approach	Income Capitalization Approach
Unobservable Input	Market Capitalization Rate	Market Capitalization Rate
Unobservable Input	Price Per Square Foot	Price Per Square Foot
Impairment of Consolidated Assets [Member] | Income Capitalization Approach [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range		12.00
Impairment of Consolidated Assets [Member] | Income Capitalization Approach [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range		117.00
Impairment of Consolidated Assets [Member] | Income Capitalization Approach [Member] | Market Capitalization Rate [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	8.00%
Impairment of Consolidated Assets [Member] | Income Capitalization Approach [Member] | Market Capitalization Rate [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range		8.00%
Impairment of Consolidated Assets [Member] | Income Capitalization Approach [Member] | Market Capitalization Rate [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range		10.00%
Impairment of Consolidated Assets [Member] | Indicative Bid/Contracted Price [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	44.6	88.7
Valuation Technique	Indicative Bid / Contracted Price	Indicative Bid /Contracted Price
Unobservable Input	Indicative Bid/ Contracted Price	Indicative Bid/ Contracted Price
Impairment of Joint Venture Investments [Member] | Discounted Cash Flow [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	$ 26.8	$ 35.3
Valuation Technique	Discounted Cash Flow	Discounted Cash Flow
Unobservable Input	Discount Rate	Discount Rate
Unobservable Input	Terminal Capitalization Rate	Terminal Capitalization Rate
Impairment of Joint Venture Investments [Member] | Discounted Cash Flow [Member] | Discount Rates [Member] | Minimum [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	8.00%	8.00%
Impairment of Joint Venture Investments [Member] | Discounted Cash Flow [Member] | Discount Rates [Member] | Maximum [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	15.00%	15.00%
Impairment of Joint Venture Investments [Member] | Discounted Cash Flow [Member] | Terminal Capitalization Rate [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	6.00%	6.00%