Regular Quarterly Distributions Declared and Paid to Common Stockholders and Common OP Unit Non-Controlling Interests (Detail) (USD $)	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2012
Noncontrolling Interest [Line Items]
Distribution Amount Per Share	$ 0.4375	$ 0.4375	$ 0.4375	$ 0.4375	$ 0.3750	$ 0.3750	$ 0.3750	$ 0.3750	$ 0.3000	$ 0.3000	$ 0.3000	$ 0.3000	$ 0.4375
Stockholder Record Date	Dec. 14, 2012	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012	Dec. 30, 2011	Sep. 30, 2011	Jun. 24, 2011	Mar. 25, 2011	Dec. 31, 2010	Sep. 24, 2010	Jun. 25, 2010	Mar. 26, 2010
Payment Date	Dec. 28, 2012	Oct. 12, 2012	Jul. 13, 2012	Apr. 13, 2012	Jan. 13, 2012	Oct. 14, 2011	Jul. 08, 2011	Apr. 08, 2011	Jan. 14, 2011	Oct. 08, 2010	Jul. 09, 2010	Apr. 09, 2010