Consolidated Statement of Changes in Equity (USD $) In Thousands, unless otherwise specified	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Distributions in Excess of Net Income [Member]	Non-controlling Interest [Member]
Balance at Dec. 31, 2008	$ 2,899,975	$ 1,016,625	$ 1,484	$ 2,702,513	$ (8,652)	$ (867,951)	$ 55,956
Comprehensive income (loss):
Net income (loss)	(271,490)					(260,150)	(11,340)
Derivative instrument activity	3,022				3,022
Comprehensive income (loss)	(268,468)
Issuance of Limited Partner Units for acquisition	0
Issuance of common shares	551,404		752	550,652
Stock based compensation plan activity	11,257		2	13,441		(2,186)
Conversion of Limited Partner Units	0		2	590		(15)	(577)
Distributions to preferred shareholders	(73,451)					(73,451)
Distributions to common shareholders	(151,333)					(151,333)
Distributions to noncontrolling interests	(1,524)						(1,524)
Balance at Dec. 31, 2009	2,967,860	1,016,625	2,240	3,267,196	(5,630)	(1,355,086)	42,515
Comprehensive income (loss):
Net income (loss)	65,262					65,798	(536)
Derivative instrument activity	4,198				4,198
Comprehensive income (loss)	69,460
Issuance of Limited Partner Units for acquisition	0
Issuance of common shares	298,066		265	297,801
Stock based compensation plan activity	10,528		3	13,056		(2,531)
Conversion of Limited Partner Units	0		14	(8,069)			8,055
Distributions to preferred shareholders	(69,468)					(69,468)
Redemption/repurchase of preferred shares	(118,787)	(112,085)		3,736		(10,438)
Distributions to common shareholders	(162,015)					(162,015)
Distributions to noncontrolling interests	(5,741)						(5,741)
Balance at Dec. 31, 2010	2,989,903	904,540	2,522	3,573,720	(1,432)	(1,533,740)	44,293
Comprehensive income (loss):
Net income (loss)	96,309					95,565	744
Derivative instrument activity	2,419				2,419
Comprehensive income (loss)	98,728
Issuance of Limited Partner Units for acquisition	28,357						28,357
Stock based compensation plan activity	10,855		4	14,041		(3,190)
Conversion of Limited Partner Units	0		3	3,127			(3,130)
Distributions to preferred shareholders	(60,353)					(60,353)
Redemption/repurchase of preferred shares	(110,726)	(110,630)		3,700		(3,796)
Distributions to common shareholders	(171,814)					(171,814)
Distributions to noncontrolling interests	(5,292)						(5,292)
Balance at Dec. 31, 2011	$ 2,779,658	$ 793,910	$ 2,529	$ 3,594,588	$ 987	$ (1,677,328)	$ 64,972