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, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Equity Method Investments [Line Items]
Company's proportionate share of the impairment charges	$ 4.4	$ 6.6	$ 0.4
Company's share of aggregate impairment charges reclassified to discontinued operations	0.8	4.0	0.7
Investment basis value for which no income loss Recognized	0
Obligation or Intent to fund additional capital	0
Unconsolidated Joint Ventures [Member]
Schedule Of Equity Method Investments [Line Items]
Impairment charges reclassified to discontinued operations related to asset sales	11.1	49.3	56.3
Coventry II Fund JV [Member]
Schedule Of Equity Method Investments [Line Items]
Effective Ownership Percentage		20.00%
Loss on property transfer		32.6
Investment basis value for which no income loss Recognized		$ 0