Assets Held for Sale and Discontinued Operations - Additional Information (Detail)	6 Months Ended	12 Months Ended
	Jun. 30, 2013 Property sqft	Dec. 31, 2012 Property sqft
Discontinued Operations And Assets Held For Sale [Line Items]
Operating property classified as held for sale	2
Discontinued Operations [Member]
Discontinued Operations And Assets Held For Sale [Line Items]
Number of properties sold to third parties	20	200
Square footage of property	1,900,000	27,200,000