Dividends Declared and Paid on Shares of Common Stock and Noncontrolling Common Units (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, 2012	Dec. 31, 2011	Dec. 28, 2012	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012	Dec. 29, 2011
Dividend Declared [Line Items]
Dividend Period	Fourth Quarter 2012	Third Quarter 2012	Second Quarter 2012	First Quarter 2012	Fourth Quarter 2011	Third Quarter 2011	Second Quarter 2011	First Quarter 2011
Amount per Share/Unit	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.21	$ 0.17	$ 0.84	$ 0.80
Dividends Period Covered	October 1, 2012 to December 31, 2012	July 1, 2012 to September 30, 2012	April 1, 2012 to June 30, 2012	January 1, 2012 to March 31, 2012	October 1, 2011 to December 31, 2011	July 1, 2011 to September 30, 2011	April 1, 2011 to June 30, 2011	January 19, 2011 to March 31, 2011
Dividend Paid Date						Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011			Dec. 28, 2012	Sep. 28, 2012	Jun. 29, 2012	Mar. 30, 2012	Dec. 29, 2011