Discontinued Operations (Details 1) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended																12 Months Ended
		Dec. 31, 2015		Sep. 30, 2015	[2]	Jun. 30, 2015	[3]	Mar. 31, 2015	[4]	Dec. 31, 2014	[5]	Sep. 30, 2014	[6]	Jun. 30, 2014	[7]	Mar. 31, 2014	[8]	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues
Rental income																		$ 383,333	$ 361,525	$ 312,322
Other operating																		5,047	5,665	5,926
Expenses
Property operating																		140,195	134,057	122,571
General and administrative																		26,925	22,808	23,704
Depreciation																		106,530	99,384	86,239
Amortization																		10,084	10,820	10,645
Bad debt, net of recoveries																		(193)	31	172
Other Income (Expense)
Loss on extinguishment of debt		$ (28,000)																(27,998)		(29,638)
Interest expense																		(65,534)	(72,413)	(73,511)
Interest and other income, net																		389	2,637	947
Income from discontinued operations																		715	967	5,246
Impairments																		(686)	(12,029)	(9,889)
Gain on sales of real estate properties																		10,571	9,283	24,718
INCOME (LOSS) FROM DISCONTINUED OPERATIONS		$ (696)	[1]	$ 10,632		$ 330		$ 333		$ 9,013		$ (4,284)		$ (2,994)		$ (3,514)		$ 10,600	$ (1,779)	$ 20,075
Income (Loss) from Discontinued Operations per Common Share - Basic (in dollars per share)																		$ 0.11	$ (0.02)	$ 0.22
Income (Loss) from Discontinued Operations per Common Share - Diluted (in dollars per share)																		$ 0.11	$ (0.02)	$ 0.22
Discontinued Operations [Member]
Revenues
Rental income	[9]																	$ 752	$ 5,660	$ 14,202
Other operating	[9]																	0	4	9
Total Revenue	[9]																	752	5,664	14,211
Expenses
Property operating	[10]																	58	3,126	4,830
General and administrative	[10]																	0	19	26
Depreciation	[10]																	0	1,551	3,794
Amortization	[10]																	0	0	63
Bad debt, net of recoveries	[10]																	(1)	3	13
Total Expense	[10]																	57	4,699	8,726
Other Income (Expense)
Loss on extinguishment of debt	[11]																	0	0	(270)
Interest expense	[11]																	0	0	(40)
Interest and other income, net	[11]																	20	2	71
Total other income (expense)	[11]																	20	2	(239)
Income from discontinued operations																		715	967	5,246
Impairments	[12]																	(686)	(12,029)	(9,889)
Gain on sales of real estate properties	[13]																	10,571	9,283	24,718
INCOME (LOSS) FROM DISCONTINUED OPERATIONS																		$ 10,600	$ (1,779)	$ 20,075
Income (Loss) from Discontinued Operations per Common Share - Basic (in dollars per share)																		$ 0.11	$ (0.02)	$ 0.22
Income (Loss) from Discontinued Operations per Common Share - Diluted (in dollars per share)																		$ 0.11	$ (0.02)	$ 0.22

[1] The increases in net income and amounts per share for the fourth quarter of 2015 are primarily attributable to gains on sales of real estate totaling $9.1 million, partially offset by impairment charges of $0.7 million.

[2] The increases in net income and amounts per share for the third quarter of 2015 are primarily attributable to a $10.6 million gain on the sale of one property previously classified as an asset held for sale.

[3] The increases in net income and amounts per share for the second quarter of 2015 are primarily attributable to a $41.5 million gain on the sale of two properties, partially offset by a $28.0 million loss on extinguishment of the Senior Notes due 2017.

[4] The decreases in net income and amounts per share for the first quarter of 2015 are primarily attributable to impairment charges of $3.3 million

[5] 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.

[6] The decreases in net income and amounts per share for the third quarter of 2014 are primarily attributable to impairment charges of $4.5 million.

[7] 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.

[8] 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.

[9] Total revenues for the years ended December 31, 2015, 2014 and 2013 included $0.8 million, $5.7 million and $14.0 million, respectively, related to properties sold; and $0.2 million related to one property held for sale as of December 31, 2013.

[10] Total expenses for the years ended December 31, 2015, 2014 and 2013 included $0.1 million, $4.7 million and $8.7 million, respectively, related to properties sold.

[11] Other income (expense) for the years ended December 31, 2015, 2014, and 2013 included income (expense) related to properties sold.

[12] Impairments for the year ended December 31, 2015 included $0.7 million related to one property held for sale. December 31, 2014 included $3.7 million related to the sale of three properties and $8.3 million on four properties, classified as held for sale and subsequently sold in 2015; 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 in 2014; and $6.2 million related to three properties held for sale

[13] Gain on sales of real estate properties for the years ended December 31, 2015, 2014 and 2013 included gains on the sale of one, three, and 12 properties, respectively.