Real Estate Assets (Details) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) propertyUnit	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Dispositions [Abstract]
Gains on disposition of property	$ 3,515		$ 3	$ 10,218	$ 16,975
Impairments [Abstract]
Impairments of real estate assets	5,318		$ 0	$ 5,849	$ 0
Raleigh NC Land Acquisition (7/2019) [Member]
Acquisitions [Abstract]
Acquisition purchase price	6,600
2019 Dispositions [Member]
Dispositions [Abstract]
Number of buildings sold | propertyUnit		2
Purchase price of real estate	14,300	$ 32,500
Gains on disposition of property	3,500	6,700
2019 Impairments [Member]
Impairments [Abstract]
Impairments of real estate assets	$ 5,300	$ 500