Consolidated Statements of Beneficiaries' Equity (USD $) In Thousands, except Share data	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Deferred Compensation, Share-based Payments [Member]	Common Stock In Grantor Trust [Member]	Cumulative Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Cumulative Distributions [Member]	Noncontrolling Interest [Member]
Beginning Balance at Dec. 31, 2012	$ 1,773,516	$ 40	$ 1,434	$ 2,780,194	$ 5,352	$ (5,352)	$ 479,734	$ (15,918)	$ (1,493,206)	$ 21,238
Beginning Balance, Shares at Dec. 31, 2012		4,000,000	143,538,733		290,745
Net income	22,187						21,992			195
Comprehensive Income (Loss)	10,210							10,093		117
Stock Issued During Period, Shares, New Issues			12,650,000
Stock Issued During Period, Value, New Issues	182,034		127	181,907
Equity Issuance Costs	(382)			(382)
Conversion of LP Units to Common Shares			81,998
Bonus Share Issuance, Shares			27,918
Stock Issued During Period, Value, Conversion of Units	0		1	1,240						(1,241)
Bonus Share Issuance, Value	361			361
Share Based Compensation Activity, Shares			409,979		34,117
Share Based Compensation Activity, Value	8,034		3	8,022			9
Share Issuance from/to Deferred Compensation Plan, Shares			(4,838)		(11,839)
Share issuance from/to Deferred Compensation Plan, Value	0				79	(79)
Adjustments to Non-controlling Interest	0			(766)						766
Preferred Share distributions	(5,175)								(5,175)
Distributions declared ($0.45 per share)	(69,627)								(68,821)	(806)
Ending Balance at Sep. 30, 2013	1,921,158	40	1,565	2,970,576	5,431	(5,431)	501,735	(5,825)	(1,567,202)	20,269
Ending Balance, Shares at Sep. 30, 2013		4,000,000	156,703,790		313,023
Beginning Balance at Dec. 31, 2013	1,921,435	40	1,566	2,971,596	5,407	(5,407)	522,528	(2,995)	(1,592,515)	21,215
Beginning Balance, Shares at Dec. 31, 2013		4,000,000	156,731,993		312,280
Net income	8,811						8,754			57
Comprehensive Income (Loss)	335							337		(2)
Common Stock, Shares, Issued	178,982,369
Stock Issued During Period, Shares, New Issues	21,850,000		21,850,000
Stock Issued During Period, Value, New Issues	335,398		219	335,179
Equity Issuance Costs	(452)			(452)
Conversion of LP Units to Common Shares			41,734
Stock Issued During Period, Value, Conversion of Units	0			655						(655)
Share Based Compensation Activity, Shares			279,913
Share Based Compensation Activity, Value	4,614		5	4,597			12
Share Issuance from/to Deferred Compensation Plan, Shares			78,729		72,256
Share issuance from/to Deferred Compensation Plan, Value	(90)			(90)	812	(812)
Adjustments to Non-controlling Interest	0			(1,172)						1,172
Preferred Share distributions	(5,175)								(5,175)
Distributions declared ($0.45 per share)	(74,986)								(74,198)	(788)
Ending Balance at Sep. 30, 2014	$ 2,189,890	$ 40	$ 1,790	$ 3,310,313	$ 6,219	$ (6,219)	$ 531,294	$ (2,658)	$ (1,671,888)	$ 20,999
Ending Balance, Shares at Sep. 30, 2014		4,000,000	178,982,369		384,536