Consolidated Statements of Beneficiaries' Equity (USD $) In Thousands, except Share data	Total	Preferred Stock [Member]	Common Stock	Deferred Compensation Payable in Common Shares	Common Shares in Grantor Trust	Additional Paid-in Capital	Cumulative Earnings	Accumulated Other Comprehensive Income (Loss)	Cumulative Distributions	Non-Controlling Interests	Subsidiaries [Member]	Subsidiaries [Member] Accumulated Other Comprehensive Income (Loss)	Subsidiaries [Member] Non-Controlling Interests	Subsidiaries [Member] Series D Preferred Stock [Member]	Subsidiaries [Member] Total partners equity [Member]	Subsidiaries [Member] Series E-linked Preferred Stock [Member]
Beginning Balance at Dec. 31, 2011	$ 1,889,696	$ 43	$ 1,424	$ 5,631	$ (5,631)	$ 2,776,197	$ 477,338	$ (6,079)	$ (1,392,332)	$ 33,105		$ (6,426)		$ 47,912	$ 1,851,326	$ 0
Beginning Balance, shares at Dec. 31, 2011		4,300,000	142,690,755	292,646										2,000,000		0
Net income (loss)	6,529						6,595			(66)	6,529				6,529
Comprehensive income (loss)	(10,026)							(9,839)		(187)	(10,026)	(10,026)			(10,026)
Issuance of Common Shares of Beneficial Interest, shares		4,000,000														4,000,000
Issuance of Common Shares of Beneficial Interest	96,850	40				96,810									96,850	96,850
Preferred share issuance costs	(613)					(613)									(613)
Redemption of preferred shares	(103,448)	(43)				(103,405)								(47,912)	(103,450)
Conversion of LP Units to Common Shares	(167)		1			149	(49)			(268)					(49)
Stock Issued During Period, Shares, Other			35,703
Conversion of LP Units to Common Shares, shares			20,464
Redemption of preferred shares, Shares		(4,300,000)												(2,000,000)
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures			797,375	9,036
Conversion of LP units to cash	(9,741)						(4,185)			(5,556)					(9,741)
Share Issuance from/to Deferred Compensation Plan, shares			(5,564)	(10,937)
Share Issuance from/to Deferred Compensation Plan	0			(279)	279
Bonus share issuance	387					387									387
Share-based compensation activity	6,432		9			6,388	35								6,432
Adjustment to Non-controlling Interest	0					4,281				(4,281)
Preferred Share distributions	(10,405)								(10,405)						(10,405)
Preferred share/unit redemption charge	(4,052)								(4,052)		(4,052)				(4,052)
Distributions declared ($0.60) per share in each of 2014, 2013, and 2012	(87,926)								(86,417)	(1,509)
Ending Balance at Dec. 31, 2012	1,773,516	40	1,434	5,352	(5,352)	2,780,194	479,734	(15,918)	(1,493,206)	21,238		(16,452)	0	0	1,746,739	96,850
Ending Balance, shares at Dec. 31, 2012		4,000,000	143,538,733	290,745										0		4,000,000
Net income (loss)	43,189						42,777			412	43,189				43,189
Comprehensive income (loss)	13,075							12,923		152	13,075	13,075			13,075
Issuance of Common Shares of Beneficial Interest, shares			12,650,000
Issuance of Common Shares of Beneficial Interest	182,034		127			181,907
Preferred share issuance costs	(744)					(744)
Noncontrolling Interest, Increase from Business Combination	946									946			946		946
Conversion of LP Units to Common Shares	0		1			1,239				(1,240)					1,240
Stock Issued During Period, Shares, Other			27,918
Conversion of LP Units to Common Shares, shares			81,998
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures			438,356	34,117
Share Issuance from/to Deferred Compensation Plan, shares			(5,012)	(12,583)
Share Issuance from/to Deferred Compensation Plan	0			55	(55)
Bonus share issuance	361					361									361
Share-based compensation activity	9,438		4			9,417	17								9,437
Adjustment to Non-controlling Interest	0					(778)				778
Preferred Share distributions	(6,900)								(6,900)						(6,900)
Preferred share/unit redemption charge	0										0
Distributions declared ($0.60) per share in each of 2014, 2013, and 2012	(93,480)								(92,409)	(1,071)
Ending Balance at Dec. 31, 2013	1,921,435	40	1,566	5,407	(5,407)	2,971,596	522,528	(2,995)	(1,592,515)	21,215	1,894,949	(3,377)	946	0	1,894,949	96,850
Ending Balance, shares at Dec. 31, 2013		4,000,000	156,731,993	312,279										0		4,000,000
Net income (loss)	6,942						6,975			(33)	6,942		(44)		6,898
Comprehensive income (loss)	(1,630)							(1,612)		(18)	(1,630)	(1,630)			(1,630)
Issuance of Common Shares of Beneficial Interest, shares	21,850,000		21,850,000
Issuance of Common Shares of Beneficial Interest	335,398		219			335,179
Preferred share issuance costs	(495)					(495)
Conversion of LP Units to Common Shares	0		2			3,612				(3,614)					3,614
Conversion of LP Units to Common Shares, shares			228,536
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures			403,902
Share Issuance from/to Deferred Compensation Plan, shares			80,152	72,257
Share Issuance from/to Deferred Compensation Plan	(90)			812	(812)	(90)
Share Choice Plan Issuance Shares	0		(1,423)
Share-based compensation activity	6,847		6			6,857	(16)								6,847
Adjustment to Non-controlling Interest	0					(1,966)				1,966
Preferred Share distributions	(6,900)								(6,900)						(6,900)
Preferred share/unit redemption charge	0										0
Distributions declared ($0.60) per share in each of 2014, 2013, and 2012	(102,181)								(101,164)	(1,017)
Ending Balance at Dec. 31, 2014	$ 2,159,326	$ 40	$ 1,793	$ 6,219	$ (6,219)	$ 3,314,693	$ 529,487	$ (4,607)	$ (1,700,579)	$ 18,499	$ 2,134,755	$ (5,007)	$ 1,010	$ 0	$ 2,134,755	$ 96,850
Ending Balance, shares at Dec. 31, 2014		4,000,000	179,293,160	384,536										0		4,000,000