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]	Subsidiary of Common Parent [Member]	Subsidiary of Common Parent [Member] Preferred Stock [Member]	Subsidiary of Common Parent [Member] Common Stock [Member]	Subsidiary of Common Parent [Member] Limited Partner [Member]	Subsidiary of Common Parent [Member] Accumulated Other Comprehensive Income (Loss) [Member]	Subsidiary of Common Parent [Member] Non-controlling Interest [Member]	Subsidiary of Common Parent [Member] Stockholders' Equity, Total [Member]
Beginning Balance - Partnership at Dec. 31, 2012								$ 2,625,951	$ 625,638	$ 1,967,091	$ 21,383	$ 2,691	$ 9,148	$ 2,616,803
Beginning Balance - General Partner at Dec. 31, 2012	2,626,118	625,638	2,794	3,953,497	2,691	(1,993,206)	34,704
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	44,123					43,525	598	44,123	9,550	33,975	392		206	43,917
Other comprehensive income	537				537			537				537		537
Issuance of common shares	574,685		416	574,269
Capital contribution from the General Partner								574,685		574,685				574,685
Stock based compensation plan activity	2,262		6	2,870		(614)		2,262		2,262				2,262
Conversion of Limited Partner Units			1	336			(337)			337	(337)
Distributions to preferred shareholders/unitholders	(9,550)					(9,550)		(9,550)	(9,550)					(9,550)
Redemption of preferred shares/units	(177,955)	(177,955)		5,932		(5,932)		(177,955)	(177,955)					(177,955)
Distributions to common shareholders	(54,678)					(54,678)
Distributions to Partners								(55,458)		(54,707)	(751)			(55,458)
Contributions from (distributions to) noncontrolling interests, net	(961)						(961)	(210)					(210)
Ending Balance - Partnership at Mar. 31, 2013								3,004,385	447,683	2,523,643	20,687	3,228	9,144	2,995,241
Ending Balance - General Partner at Mar. 31, 2013	$ 3,004,581	$ 447,683	$ 3,217	$ 4,536,904	$ 3,228	$ (2,020,455)	$ 34,004