Discontinued Operations (Details 1) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Revenues
Rental income																	$ 318,294		$ 288,787		$ 263,740
Other operating																	5,931		6,101		7,885
Total Revenue	90,116	[1]	84,311	[2]	82,062	[3]	80,437	[4]	78,250	[5]	76,481	[6]	75,487	[7]	73,856	[8]	336,926		304,074		278,598
Expenses
Property operating																	125,565		116,470		112,152
General and administrative																	23,729		20,905		20,988
Depreciation																	88,380		81,966		72,036
Amortization																	10,645		10,418		8,105
Bad debt, net of recoveries																	184		241		(251)
Total Expenses																	248,503		230,000		213,030
Other Income (Expense)
Loss on extinguishment of debt					(29,900)												(29,638)				(1,986)
Interest expense																	(73,511)		(74,955)		(75,938)
Interest and other income, net																	966		976		813
Total other income (expense)																	(100,691)		(73,979)		(77,111)
Income from discontinued operations																	4,422		9,474		11,021
Impairments																	(9,889)		(14,908)		(6,697)
Gain on sales of real estate properties	2,700		20,200		1,800				1,200		6,300				3,400		24,718		10,874		7,035
Discontinued operations	2,568	[1]	15,080	[2]	3,463	[3]	(1,860)	[4]	(4,895)	[5]	5,200	[6]	2,053	[7]	3,082	[8]	19,251		5,440		11,359
Income (Loss) from Discontinued Operations per Common Share - Basic																	$ 0.21		$ 0.07		$ 0.16
Income (Loss) from Discontinued Operations per Common Share - Diluted																	$ 0.21		$ 0.07		$ 0.16
Discontinued Operations [Member]
Revenues
Rental income																	8,229	[9]	17,947	[9]	23,628	[9]
Other operating																	4	[9]	20	[9]	56	[9]
Total Revenue																	8,233	[9]	17,967	[9]	23,684	[9]
Expenses
Property operating																	1,836	[10]	3,712	[10]	5,433	[10]
General and administrative																	1	[10]	9	[10]	10	[10]
Depreciation																	1,653	[10]	4,698	[10]	7,019	[10]
Amortization																	63	[10]	147	[10]	121	[10]
Bad debt, net of recoveries																	1	[10]	(1)	[10]	91	[10]
Total Expenses																	3,554	[10]	8,565	[10]	12,674	[10]
Other Income (Expense)
Loss on extinguishment of debt																	(270)	[11]	0	[11]	0	[11]
Interest expense																	(40)	[11]	(97)	[11]	(100)	[11]
Interest and other income, net																	53	[11]	169	[11]	111	[11]
Total other income (expense)																	(257)	[11]	72	[11]	11	[11]
Income from discontinued operations																	4,422		9,474		11,021
Impairments																	(9,889)	[12]	(14,908)	[12]	(6,697)	[12]
Gain on sales of real estate properties																	24,718	[13]	10,874	[13]	7,035	[13]
Discontinued operations																	$ 19,251		$ 5,440		$ 11,359
Income (Loss) from Discontinued Operations per Common Share - Basic																	$ 0.21		$ 0.07		$ 0.16
Income (Loss) from Discontinued Operations per Common Share - Diluted																	$ 0.21		$ 0.07		$ 0.16

[1] 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.

[2] 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.

[3] 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.

[4] 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.

[5] The decreases in net income and amounts per share for the fourth quarter of 2012 are primarily attributable to impairment charges of $7.7 million. This amount is partially offset by gains on sales of real estate totaling $1.2 million.

[6] The increases in net income and amounts per share for the third quarter of 2012 are primarily attributable to gains on sales of real estate totaling $6.3 million, partially offset by impairment charges of $2.9 million.

[7] The decreases in net income and amounts per share for the second quarter of 2012 are primarily attributable to impairment charges of $0.2 million.

[8] The increases in net income and amounts per share for the first quarter of 2012 are primarily attributable to gains on sales of real estate totaling $3.4 million and a lease termination fee totaling $1.5 million which is included in discontinued operations. This amount is partially offset by impairment charges of $4.2 million.

[9] Total revenues for the years ended December 31, 2013, 2012 and 2011 included $7.0 million, $16.2 million and $22.1 million, respectively, related to properties sold; and $1.2 million, $1.8 million and $1.6 million, respectively, related to three properties held for sale as of December 31, 2013.

[10] Total expenses for the years ended December 31, 2013, 2012 and 2011 included $2.1 million, $7.4 million and $12.0 million, respectively, related to properties sold; and $1.5 million, $1.2 million and $0.7 million, respectively, related to three properties held for sale as of December 31, 2013.

[11] Other income (expense) for the years ended December 31, 2013, 2012, and 2011 included income related to properties sold.

[12] Impairments for the year ended 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 to held for sale and subsequently sold for a gain; and $6.2 million related to three properties held for sale; December 31, 2012 included $11.1 million related to 12 properties sold and $3.8 million related to one property held for sale; and December 31, 2011 included $1.7 million related to two properties sold and $5.0 million related to five properties held for sale.

[13] Gain on sales of real estate properties for the years ended December 31, 2013, 2012 and 2011 included gains on the sale of 12, seven and three properties, respectively.