Assets Held for Sale and Discontinued Operations - Additional Information (Detail) (Discontinued Operations [Member])	9 Months Ended	12 Months Ended
	Sep. 30, 2013 Property sqft	Dec. 31, 2012 Property sqft
Discontinued Operations [Member]
Discontinued Operations And Assets Held For Sale [Line Items]
Number of properties sold to third parties	39	200
Square footage of property	4,800,000	27,200,000