Equity And Noncontrolling Interests (Narrative) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended	9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended
	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 At-The-Market Common Equity Sales Program [Member]	Sep. 30, 2011 At-The-Market Common Equity Sales Program [Member]	Sep. 30, 2012 At-The-Market Common Equity Sales Program [Member]	Sep. 30, 2011 At-The-Market Common Equity Sales Program [Member]	Sep. 30, 2012 At-The-Market Common Equity Sales Program [Member] Gross [Member]	Sep. 30, 2011 At-The-Market Common Equity Sales Program [Member] Gross [Member]	Sep. 30, 2012 At-The-Market Common Equity Sales Program [Member] Gross [Member]	Sep. 30, 2011 At-The-Market Common Equity Sales Program [Member] Gross [Member]	Sep. 30, 2012 At-The-Market Common Equity Sales Program [Member] Net [Member]	Sep. 30, 2011 At-The-Market Common Equity Sales Program [Member] Net [Member]	Sep. 30, 2012 At-The-Market Common Equity Sales Program [Member] Net [Member]	Sep. 30, 2011 At-The-Market Common Equity Sales Program [Member] Net [Member]	Dec. 31, 2010 Series B Preferred Stock [Member]	Mar. 31, 2011 Series B Preferred Stock [Member]
Equity And Noncontrolling Interests [Line Items]
Common stock, shares authorized		100,000,000		100,000,000	4,000		4,000
Common stock, shares issued					4,000		4,000
Sale of common stock, shares					137,000	1,323,000	550,000	2,321,000
Net proceeds contributed to the Operating Partnership in exchange of common units		$ 25,457	$ 91,722						$ 6,994	$ 54,681	$ 26,153	$ 93,736	$ 6,831	$ 53,488	$ 25,457	$ 91,722
Sales price per share					$ 51.24	$ 41.34	$ 47.55	$ 40.38
Stock repurchase program, authorized amount	200,000
Redemption of preferred stock			49,633														49,571	49,571
Redemption value of noncontrolling interest in Operating Partnership		6,874		6,840
Noncontrolling interests in the Operating Partnership, net book value		$ 2,802		$ 2,935