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	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2014
Impairment of Consolidated Assets [Member] | Income Capitalization Approach [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	75.5	67.0
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	88.7	74.2
Impairment of Joint Venture Investments [Member] | Discounted Cash Flow [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	35.3	6.4
Impairment of Joint Venture Investments [Member] | Discounted Cash Flow [Member] | Discount Rates [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range		15.00%
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%
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%
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%