Real Estate Investments - Discontinued Operations and Assets Held for Sale - Income Statement (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2015 property	Sep. 30, 2015 USD ($) property	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) property	Sep. 30, 2014 USD ($)	Dec. 31, 2014 property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties held for sale | property		2		2		2
Revenues
Rental income		$ 95,383	$ 92,095	$ 285,867	$ 267,877
Other operating		1,313	1,474	3,931	4,345
Expenses
Property operating		35,247	34,204	103,437	100,671
General and administrative		6,258	5,185	19,709	16,818
Depreciation		26,571	25,345	79,511	73,503
Bad debts, net of recoveries		(21)	3	(202)	123
Other Income (Expense)
Interest and other income, net		72	409	311	2,545
Discontinued Operations
Income from discontinued operations		61	221	725	238
Impairments of real estate assets		0	(4,505)	0	(11,034)
Gain on sale of property		10,571	0	10,571	3
INCOME (LOSS) FROM DISCONTINUED OPERATIONS		10,632	(4,284)	11,296	(10,793)
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties held for sale | property						2
Number of held-for-sale properties sold | property	1
Revenues
Rental income		62	1,357	752	4,326
Other operating		0	1	0	4
Revenues		62	1,358	752	4,330
Expenses
Property operating		2	724	48	2,631
General and administrative		0	6	0	18
Depreciation		0	419	0	1,449
Bad debts, net of recoveries		(1)	(4)	(1)	3
Total Expenses		1	1,145	47	4,101
Other Income (Expense)
Interest and other income, net		0	8	20	9
Total other income (expense)		0	8	20	9
Discontinued Operations
Income from discontinued operations		61	221	725	238
Impairments of real estate assets		0	(4,505)	0	(11,034)
Gain on sale of property		10,571	0	10,571	3
INCOME (LOSS) FROM DISCONTINUED OPERATIONS		$ 10,632	$ (4,284)	$ 11,296	$ (10,793)