CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (Unaudited) (USD $) In Thousands, unless otherwise specified	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]
Beginning Balance at Dec. 31, 2012	$ 1,333,165	$ 243,790	$ 18	$ 2,212,949	$ (1,143,803)	$ (6,224)	$ 26,435
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units for common shares	0	0	0	887	0	0	(887)
Repurchase of preferred shares	(155,004)	(149,774)	0	0	(5,230)	0	0
Issuance of common shares upon conversion of convertible notes	60,686	0	1	60,685	0	0	0
Issuance of common shares and deferred compensation amortization, net	313,230	0	3	313,227	0	0	0
Acquisition of consolidated joint venture partner's equity interest	(8,918)	0	0	0	(8,918)	0	0
Dividends/distributions	(107,807)	0	0	0	(104,904)	0	(2,903)
Net income	10,864	0	0	0	8,807	0	2,057
Other comprehensive loss	8,523	0	0	0	0	8,523	0
Ending Balance at Sep. 30, 2013	1,454,739	94,016	22	2,587,748	(1,254,048)	2,299	24,702
Beginning Balance at Dec. 31, 2013	1,539,483	94,016	23	2,717,787	(1,300,527)	4,439	23,745
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units	(1,962)	0	0	(950)	0	0	(1,012)
Issuance of common shares upon conversion of convertible notes	4,834	0	0	4,834	0	0	0
Issuance of common shares and deferred compensation amortization, net	25,594	0	0	25,594	0	0	0
Acquisition of consolidated joint venture partner's equity interest	(2,100)	0	0	0	(2,262)	0	162
Dividends/distributions	(124,018)	0	0	0	(121,137)	0	(2,881)
Net income	59,278	0	0	0	55,741	0	3,537
Other comprehensive loss	(1,134)	0	0	0	0	(1,134)	0
Ending Balance at Sep. 30, 2014	$ 1,499,975	$ 94,016	$ 23	$ 2,747,265	$ (1,368,185)	$ 3,305	$ 23,551