Impairment Charges and Impairment of Joint Venture Investments - Summary of Significant Unobservable Inputs (Detail) (Level 3 [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013	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	22.0	136.6
Valuation Technique	Indicative Bid	Indicative Bid
Unobservable Input	Indicative Bid	Indicative Bid
Range
Impairment of consolidated assets - Held for Sale, Contracted Price [Member]
Fair Value Assets And Liabilities Measured On Nonrecurring Basis [Line Items]
Fair Value	7.3
Valuation Technique	Contracted Price
Unobservable Input	Contracted Price
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%