Investments in and Advances to Joint Ventures - Condensed Combined Statements of Operations of Unconsolidated Joint Venture Investments (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]
Company's proportionate share of the impairment charges	$ 0.6	$ 6.7
Impairment charges reclassified to discontinued operations related to asset sales	46.8	63.6	21.0
Company's share of aggregate impairment charges reclassified to discontinued operations	$ 0.5	$ 6.3	$ 0.7