Discontinued Operations (Details 1) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Revenues
Rental income																	$ 361,525		$ 312,322		$ 282,444
Other operating																	5,665		5,926		6,052
Total Revenue	95,001	[1]	93,612	[2]	91,671	[3]	90,571	[4]	88,622	[5]	82,805	[6]	80,552	[7]	78,970	[8]	370,855		330,949		297,682
Expenses
Property operating																	134,057		122,571		113,287
General and administrative																	22,808		23,704		20,881
Depreciation																	99,384		86,239		79,776
Amortization																	10,820		10,645		10,418
Bad debt, net of recoveries																	31		172		230
Total Expenses																	267,100		243,331		224,592
Other Income (Expense)
Loss on extinguishment of debt													29,900						(29,638)
Interest expense																	(72,413)		(73,511)		(74,955)
Interest and other income, net																	2,637		947		973
Total other income (expense)																	(69,776)		(100,710)		(73,982)
Income from discontinued operations																	967		5,246		10,461
Impairments																	(12,029)		(9,889)		(14,908)
Gain on sales of real estate properties	9,300								2,700		20,200		1,800				9,283		24,718		10,874
Discontinued operations	9,013	[1]	(4,284)	[2]	(2,994)	[3]	(3,514)	[4]	2,800	[5]	15,272	[6]	3,623	[7]	(1,620)	[8]	(1,779)		20,075		6,427
Income (Loss) from Discontinued Operations per Common Share - Basic (in dollars per share)																	$ (0.02)		$ 0.22		$ 0.08
Income (Loss) from Discontinued Operations per Common Share - Diluted (in dollars per share)																	$ (0.02)		$ 0.22		$ 0.08
Discontinued Operations [Member]
Revenues
Rental income																	5,660	[9]	14,202	[9]	24,290	[9]
Other operating																	4	[9]	9	[9]	69	[9]
Total Revenue																	5,664	[9]	14,211	[9]	24,359	[9]
Expenses
Property operating																	3,126	[10]	4,830	[10]	6,894	[10]
General and administrative																	19	[10]	26	[10]	33	[10]
Depreciation																	1,551	[10]	3,794	[10]	6,888	[10]
Amortization																	0	[10]	63	[10]	147	[10]
Bad debt, net of recoveries																	3	[10]	13	[10]	10	[10]
Total Expenses																	4,699	[10]	8,726	[10]	13,972	[10]
Other Income (Expense)
Loss on extinguishment of debt																	0	[11]	(270)	[11]	0	[11]
Interest expense																	0	[11]	(40)	[11]	(97)	[11]
Interest and other income, net																	2	[11]	71	[11]	171	[11]
Total other income (expense)																	2	[11]	(239)	[11]	74	[11]
Income from discontinued operations																	967		5,246		10,461
Impairments																	(12,029)	[12]	(9,889)	[12]	(14,908)	[12]
Gain on sales of real estate properties																	9,283	[13]	24,718	[13]	10,874	[13]
Discontinued operations																	$ (1,779)		$ 20,075		$ 6,427
Income (Loss) from Discontinued Operations per Common Share - Basic (in dollars per share)																	$ (0.02)		$ 0.22		$ 0.08
Income (Loss) from Discontinued Operations per Common Share - Diluted (in dollars per share)																	$ (0.02)		$ 0.22		$ 0.08

[1] The increases in net income and amounts per share for the fourth quarter of 2014 are primarily attributable to gains on sales of real estate totaling $9.3 million, partially offset by impairment charges of $1.0 million.

[2] The decreases in net income and amounts per share for the third quarter of 2014 are primarily attributable to impairment charges of

[3] The increases in net income and amounts per share for the second quarter of 2014 are primarily attributable to a $1.9 million cash reimbursement received by the Company for certain operating expenses paid by the Company for years 2006 through 2013

[4] The decreases in net income and amounts per share for the first quarter of 2014 are primarily attributable to impairment charges of $3.4 million.

[5] The increases in net income and amounts per share for the fourth quarter of 2013 are primarily attributable to gains on sales of real estate totaling $2.7 million.

[6] The increases in net income and amounts per share for the third quarter of 2013 are primarily attributable to gains on sales of real estate totaling $20.2 million, partially offset by impairment charges of $6.3 million.

[7] The decreases in net income and amounts per share for the second quarter of 2013 are primarily attributable to losses of extinguishment of debt of $29.9 million, of which $0.3 million is included in discontinued operations. This amount is partially offset by gains on sales of real estate totaling $1.8 million.

[8] The decreases in net income and amounts per share for the first quarter of 2013 are primarily attributable to impairment charges of $3.6 million.

[9] Total revenues for the years ended December 31, 2014, 2013 and 2012 included $4.3 million, $12.6 million and $22.2 million, respectively, related to properties sold; and $1.4 million, $1.6 million and $2.2 million, respectively, related to two properties held for sale as of December 31, 2014.

[10] Total expenses for the years ended December 31, 2014, 2013 and 2012 included $4.7 million, $8.7 million and $13.5 million, respectively, related to properties sold; and for the year ended December 31, 2012 included $0.5 million related to two properties held for sale as of December 31, 2014.

[11] Other income (expense) for the years ended December 31, 2014, 2013, and 2012 included income (expense) related to properties sold.

[12] Impairments for the year ended December 31, 2014 included $3.7 million in connection with the sale of three properties and $8.3 million on two properties in held for sale and two properties there were reclassified to held for sale during 2014. All four properties of these were subsequently sold; December 31, 2013 included the following: $3.3 million related to the sale of a land parcel; $0.4 million related to two properties classified as held for sale and subsequently sold for a gain; and $6.2 million related to three properties held for sale; and December 31, 2012 included $11.1 million related to 12 properties sold and $3.8 million related to one properties held for sale.

[13] Gain on sales of real estate properties for the years ended December 31, 2014, 2013 and 2012 included gains on the sale of three, 12 and seven properties, respectively.