CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (Unaudited) (USD $) In Thousands	Total	Preferred Shares [Member]	Common Shares [Member]	Additional Paid-in-Capital [Member]	Accumulated Distributions in Excess of Net Income [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non-controlling Interests [Member]
Balance at Dec. 31, 2011	$ 1,170,203	$ 311,673	$ 15	$ 2,010,850	$ (1,212,630)	$ 1,938	$ 58,357
Repurchase of preferred shares	(1,461)	(1,690)	0	0	229	0	0
Issuance of common shares and deferred compensation amortization, net	3,119	0	1	3,118	0	0	0
Contributions from noncontrolling interests	889	0	0	0	0	0	889
Dividends/distributions	(26,494)	0	0	0	(25,276)	0	(1,218)
Net income (loss)	5,478	0	0	0	3,611	0	1,867
Other comprehensive income (loss)	(56)	0	0	0	0	(56)	0
Balance at Mar. 31, 2012	1,151,678	309,983	16	2,013,968	(1,234,066)	1,882	59,895
Balance at Dec. 31, 2012	1,333,165	243,790	18	2,212,949	(1,143,803)	(6,224)	26,435
Redemption of noncontrolling OP units for common shares	0	0	0	458	0	0	(458)
Repurchase of preferred shares	47,128	0	0	47,128	0	0	0
Issuance of common shares and deferred compensation amortization, net	300,130	0	3	300,127	0	0	0
Dividends/distributions	(37,448)	0	0	0	(36,546)	0	(902)
Net income (loss)	(2,123)	0	0	0	(2,620)	0	497
Other comprehensive income (loss)	702	0	0	0	0	702	0
Balance at Mar. 31, 2013	$ 1,641,554	$ 243,790	$ 21	$ 2,560,662	$ (1,182,969)	$ (5,522)	$ 25,572