Real Estate Assets (Property Dispositions and Real Estate Assets Held for Sale) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) property	Jun. 30, 2017 USD ($) property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from disposition of properties			$ 17,425,000	$ 16,973,000
Gain on disposition of real estate, net	$ 1,987,000	$ 1,452,000	$ 2,251,000	$ 1,452,000
Property Disposition 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | property			12
Aggregate gross sales price			$ 17,900,000
Proceeds from disposition of properties			17,400,000
Gain on disposition of real estate, net			2,300,000
Property Dispositions, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | property				11
Aggregate gross sales price				$ 17,700,000
Proceeds from disposition of properties				17,000,000
Gain on disposition of real estate, net				1,500,000
Affiliated entity | Disposition fee | Property Disposition 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposition fees paid			$ 0
Affiliated entity | Disposition fee | Property Dispositions, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposition fees paid				$ 0