Financial Information for Operation Segments (Parenthetical) (Detail) (Home Sales and Rentals Operations segment, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Home Sales and Rentals Operations segment
Segment Reporting Information [Line Items]
Site rental income	$ 36.2	$ 23.9	$ 15.3