Real Estate Assets (Details) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2020 USD ($) propertyUnit	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($) propertyUnit shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) propertyUnit	Sep. 30, 2019 USD ($)
Dispositions [Abstract]
Gain/(loss) on disposition of property	$ 10,012			$ 3,515	$ 163,397	$ 10,218
Impairments [Abstract]
Impairments of real estate assets	$ 0			$ 5,318	$ 1,778	$ 5,849
Raleigh NC Land Acquisition [Member]
Acquisitions [Abstract]
Acquisition purchase price		$ 2,300
Nashville TN Land Acquisition [Member]
Acquisitions [Abstract]
Acquisition purchase price			$ 6,200
Issuance of Common Units in acquisition (in units) | shares			118,592
2020 Dispositions [Member]
Dispositions [Abstract]
Number of buildings sold | propertyUnit	2		41		2
Purchase price of real estate	$ 23,300	2,800	$ 338,400
Closing credits excluded for unfunded building and/or tenant improvements			3,800
Gain/(loss) on disposition of property	9,400	(100)	$ 153,100
1st Quarter Disposition of Property [Member]
Dispositions [Abstract]
Gain/(loss) on disposition of property	$ 600
2016 Land Disposition [Member]
Dispositions [Abstract]
Gain/(loss) on disposition of property		400
2020 Impairments [Member]
Impairments [Abstract]
Impairments of real estate assets		$ 1,800