Acquisitions and Dispositions - Assets Held for Sale (Details) $ in Thousands	Jun. 30, 2018 USD ($) properties portfolio	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Line Items]
Number of portfolios comprised of properties held for sale | portfolio	1
Number of properties, held for sale | properties	17
Real estate held for sale before accumulated deprecation	$ 129,143
Accumulated depreciation	(17,732)
Real estate held for sale	111,411	$ 0
Land and improvements
Property, Plant and Equipment [Line Items]
Real estate held for sale before accumulated deprecation	12,856
Building and improvements
Property, Plant and Equipment [Line Items]
Real estate held for sale before accumulated deprecation	91,510
Tenant improvements
Property, Plant and Equipment [Line Items]
Real estate held for sale before accumulated deprecation	67
Acquired lease intangibles
Property, Plant and Equipment [Line Items]
Real estate held for sale before accumulated deprecation	21,802
Other assets
Property, Plant and Equipment [Line Items]
Real estate held for sale before accumulated deprecation	$ 2,908