Real Estate Assets (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2021 USD ($) parcel	Dec. 31, 2021 USD ($) ft² numberOfLoans numberOfOfficeBuildings numberOfBuildings	Dec. 31, 2020 USD ($) a numberOfBuildings parcel shares	Dec. 31, 2019 USD ($) ft² a parcel numberOfBuildings
Acquisitions [Abstract]
Rentable square feet of commercial real estate (in square feet) | ft²		28,000,000
Percentage of equity interest in joint ventures, maximum		50.00%
Dispositions [Abstract]
Gains on disposition of property		$ 174,059	$ 215,897	$ 39,517
Impairments [Abstract]
Impairments of real estate assets		0	1,778	5,849
PAC Portfolio Acquisition [Member]
Acquisitions [Abstract]
Purchase price of acquisition		653,600
Capitalized acquisition costs		$ 4,500
Number of loans assumed in acquisition | numberOfLoans		4
150 Fayetteville Asset [Member]
Acquisitions [Abstract]
Rentable square feet of commercial real estate (in square feet) | ft²		560,000
CAPTRUST Towers Asset [Member]
Acquisitions [Abstract]
Rentable square feet of commercial real estate (in square feet) | ft²		300,000
Capitol Towers Asset [Member]
Acquisitions [Abstract]
Rentable square feet of commercial real estate (in square feet) | ft²		479,000
Morrocroft Centre Asset [Member]
Acquisitions [Abstract]
Rentable square feet of commercial real estate (in square feet) | ft²		291,000
Nashville TN Land Acquisitions [Member]
Acquisitions [Abstract]
Purchase price of acquisition	$ 16,000	$ 74,100
Number of development parcels acquired (in parcels) | parcel	1
Forum Portfolio Acquisition [Member]
Acquisitions [Abstract]
Purchase price of acquisition		$ 131,300
Percentage of partner's interest in asset acquired (in hundredths)		75.00%
Number of office properties acquired | numberOfOfficeBuildings		5
Rentable square feet of commercial real estate (in square feet) | ft²		636,000
Percentage of equity interest in joint ventures, maximum		25.00%
2020 Land Acquisitions [Member]
Acquisitions [Abstract]
Purchase price of acquisition			$ 8,500
Number of development parcels acquired (in parcels) | parcel			2
Undeveloped land suitable for future development (in acres) | a			1
Issuance of Common Units in acquisition (in units) | shares			118,592
Submarket Acquisition [Member]
Acquisitions [Abstract]
Purchase price of acquisition				$ 399,100
Rentable square feet of commercial real estate (in square feet) | ft²				841,000
2019 Land Acquisitions [Member]
Acquisitions [Abstract]
Purchase price of acquisition				$ 12,400
Number of development parcels acquired (in parcels) | parcel				4
Undeveloped land suitable for future development (in acres) | a				10
2021 Dispositions [Member]
Dispositions [Abstract]
Number of buildings sold | numberOfBuildings		13
Sale price of disposition		$ 384,600
Closing credits excluded for unfunded building and/or tenant improvements		6,900
Gains on disposition of property		$ 172,800
2020 Dispositions [Member]
Dispositions [Abstract]
Number of buildings sold | numberOfBuildings			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 | numberOfBuildings				6
Sale price of disposition				$ 136,400
Gains on disposition of property				39,500
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