Impairment Charges and Impairment of Joint Venture Investments - Summary of Significant Unobservable Inputs (Detail) (Level 3 [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Impairment of consolidated assets, Income Capitalization Approach [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	$ 44.1
Valuation Technique	Income Capitalization Approach
Unobservable Input	Market Capitalization Rate
Impairment of consolidated assets, Income Capitalization Approach [Member] | Fair Value Measurements [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Unobservable Input	Price Per Square Foot
Impairment of consolidated assets, Indicative Bid [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	136.6
Valuation Technique	Indicative Bid
Unobservable Input	Indicative Bid
Range
Impairment of joint venture investments, Income Capitalization Approach [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	4.7
Valuation Technique	Income Capitalization Approach
Unobservable Input	Market Capitalization Rate
Range	8.00%
Impairment of joint venture investments, Discounted Cash Flow [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	0
Valuation Technique	Discounted Cash Flow
Unobservable Input	Discount Rate
Range	11.00%
Impairment of joint venture investments, Discounted Cash Flow [Member] | Fair Value Measurements [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Unobservable Input	Terminal Capitalization Rate
Deconsolidated joint venture investment, Discounted Cash Flow [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	$ 56.1
Valuation Technique	Discounted Cash Flow
Unobservable Input	Discount Rate
Minimum [Member] | Impairment of consolidated assets, Income Capitalization Approach [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	8.00%
Minimum [Member] | Impairment of consolidated assets, Income Capitalization Approach [Member] | Fair Value Measurements [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range (per square foot)	15
Minimum [Member] | Impairment of joint venture investments, Discounted Cash Flow [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	5.50%
Minimum [Member] | Deconsolidated joint venture investment, Discounted Cash Flow [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	8.00%
Maximum [Member] | Impairment of consolidated assets, Income Capitalization Approach [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	12.00%
Maximum [Member] | Impairment of consolidated assets, Income Capitalization Approach [Member] | Fair Value Measurements [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range (per square foot)	47
Maximum [Member] | Impairment of joint venture investments, Discounted Cash Flow [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	8.50%
Maximum [Member] | Deconsolidated joint venture investment, Discounted Cash Flow [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Range	15.00%