Noncontrolling Interest - Holders of Convertible Limited Partnership Units in Operating Partnership - Additional Information (Detail) (Noncontrolling Interest) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Noncontrolling Interest
Noncontrolling Interest [Line Items]
Percentage of ownership interest of noncontrolling interest	25.40%		25.40%
Limited partnership units	6.9		6.9
Limited partnership units, conversion ratio	1		1
Outstanding stock percent that should be acquired for rights to be exercised	39.90%		39.90%
Limited partnership units convertible in to shares of common stock, eligible for conversion	1.25		1.25
Fully converted partnership units and diluted weighted average shares outstanding	27.2	26.5	27.2	26.4