Held for Sale and Discontinued Operations (Details 1) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Rental income									$ 422,852	$ 407,481	$ 383,333
Other operating									1,647	4,149	5,047
Expenses
Property operating									157,233	146,458	140,195
Bad debt, net of recoveries									169	(21)	(193)
Other Income (Expense)
Interest and other income, net									896	375	389
Income from discontinued operations									(9)	(71)	715
Impairments										(121)	(686)
Gain on sales of real estate properties									5	7	10,571
INCOME (LOSS) FROM DISCONTINUED OPERATIONS	$ 0	$ 8	$ 0	$ (13)	$ (143)	$ (23)	$ (12)	$ (7)	$ (4)	$ (185)	$ 10,600
Income (Loss) from Discontinued Operations per Common Share - Basic (in dollars per share)									$ 0.00	$ 0.00	$ 0.11
Income (Loss) from Discontinued Operations per Common Share - Diluted (in dollars per share)									$ 0.00	$ 0.00	$ 0.11
Discontinued Operations [Member]
Revenues
Rental income									$ 0	$ 0	$ 752
Other operating									0	0	0
Total Revenue									0	0	752
Expenses
Property operating									19	71	58
Bad debt, net of recoveries									(10)	0	(1)
Total Expense									9	71	57
Other Income (Expense)
Interest and other income, net									0	0	20
Total other income (expense)									0	0	20
Income from discontinued operations									(9)	(71)	715
Impairments									0	(121)	(686)
Gain on sales of real estate properties									5	7	10,571
INCOME (LOSS) FROM DISCONTINUED OPERATIONS									$ (4)	$ (185)	$ 10,600
Income (Loss) from Discontinued Operations per Common Share - Basic (in dollars per share)									$ 0.00	$ 0.00	$ 0.11
Income (Loss) from Discontinued Operations per Common Share - Diluted (in dollars per share)									$ 0.00	$ 0.00	$ 0.11