Real Estate Assets (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) a ft² propertyUnit parcel shares	Dec. 31, 2019 USD ($) ft² a propertyUnit parcel	Dec. 31, 2018 USD ($) a propertyUnit parcel
Acquisitions [Abstract]
Rentable square feet of commercial real estate (in square feet) | ft²	27,200,000
Undeveloped land suitable for future development (in acres) | a	230
Dispositions [Abstract]
Gains on disposition of property	$ 215,897	$ 39,517	$ 37,638
Impairments [Abstract]
Impairments of real estate assets	$ 1,778	$ 5,849	$ 423
2020 Land Acquisitions [Member]
Acquisitions [Abstract]
Number of development parcels acquired (in parcels) | parcel	2
Undeveloped land suitable for future development (in acres) | a	1
Purchase price of acquisition	$ 8,500
Issuance of Common Units in acquisition (in units) | shares	118,592
Submarket Acquisition [Member]
Acquisitions [Abstract]
Rentable square feet of commercial real estate (in square feet) | ft²		841,000
Purchase price of acquisition		$ 399,100
2019 Land Acquisitions [Member]
Acquisitions [Abstract]
Number of development parcels acquired (in parcels) | parcel		4
Undeveloped land suitable for future development (in acres) | a		10
Purchase price of acquisition		$ 12,400
Nashville TN Land Acquisition (03/2018) [Member]
Acquisitions [Abstract]
Number of development parcels acquired (in parcels) | parcel			2
Undeveloped land suitable for future development (in acres) | a			9
Purchase price of acquisition			$ 50,600
2020 Dispositions [Member]
Acquisitions [Abstract]
Rentable square feet of commercial real estate (in square feet) | ft²	4,489,000
Dispositions [Abstract]
Number of buildings sold | propertyUnit	52
Sale price of disposition	$ 494,200
Closing credits excluded for unfunded building and/or tenant improvements	5,700
Gains on disposition of property	215,500
2019 Dispositions [Member]
Dispositions [Abstract]
Number of buildings sold | propertyUnit		6
Sale price of disposition		$ 136,400
Gains on disposition of property		39,500
2018 Dispositions [Member]
Dispositions [Abstract]
Number of buildings sold | propertyUnit			3
Sale price of disposition			$ 90,600
Gains on disposition of property			37,600
2016 Land Disposition [Member]
Dispositions [Abstract]
Gains on disposition of property	400
2020 Impairments [Member]
Impairments [Abstract]
Impairments of real estate assets	$ 1,800
2019 Impairments [Member]
Impairments [Abstract]
Impairments of real estate assets		$ 5,800
2018 Impairments [Member]
Impairments [Abstract]
Impairments of real estate assets			$ 400