Investments in and Advances to Joint Ventures - Service Fees and Income Earned by Company's Unconsolidated Joint Ventures (Detail) (Unconsolidated Joint Ventures [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Unconsolidated Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Management and other fees	$ 28.6	$ 29.8	$ 34.0
Financing and other fees	0	0.1	0.3
Development fees and leasing commissions	8.7	7.0	7.2
Interest income	$ 9.7	$ 0.1	$ 0.4