Acquisitions, Dispositions and Mortgage Repayments - Dispositions (Details) $ in Thousands														1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 23, 2021 USD ($) ft²	Dec. 22, 2021 USD ($) ft²	Dec. 08, 2021 USD ($) ft² property	Oct. 28, 2021 USD ($) ft²	Jul. 19, 2021 property	Jul. 09, 2021 USD ($) ft²	May 19, 2021 USD ($) ft² property	May 18, 2021 USD ($) ft²	Apr. 12, 2021 USD ($) ft²	Mar. 11, 2021 USD ($) ft² property	Mar. 05, 2021 property	Sep. 30, 2020 USD ($) ft²	Jul. 30, 2020 USD ($) ft²	May 31, 2020 USD ($) property	Jun. 30, 2020 property	Dec. 31, 2021 USD ($) ft² property	Dec. 31, 2020 USD ($) ft² property
Real Estate Dispositions [Line Items]
SALES PRICE														$ 244,500		$ 188,400	$ 249,500
CLOSING ADJUSTMENTS																(4,229)	(200)
NET PROCEEDS																184,171	249,300
NET REAL ESTATE INVESTMENT																132,356	171,800
OTHER including receivables																7,981	7,100
GAIN/ (IMPAIRMENT)																$ 43,834	$ 70,400
SQUARE FOOTAGE unaudited | ft²																847,002	412,000
Number of properties sold | property														2		5
Number of land parcels held for development | property																7	8
Los Angeles, CA | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE										$ 26,000
CLOSING ADJUSTMENTS										(555)
NET PROCEEDS										25,445
NET REAL ESTATE INVESTMENT										6,046
OTHER including receivables										509
GAIN/ (IMPAIRMENT)										$ 18,890
SQUARE FOOTAGE unaudited | ft²										73,906
Atlanta, GA | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE									$ 8,050
CLOSING ADJUSTMENTS									(272)
NET PROCEEDS									7,778
NET REAL ESTATE INVESTMENT									5,675
OTHER including receivables									151
GAIN/ (IMPAIRMENT)									$ 1,952
SQUARE FOOTAGE unaudited | ft²									19,732
Richmond, VA | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE								$ 52,000
CLOSING ADJUSTMENTS								(314)
NET PROCEEDS								51,686
NET REAL ESTATE INVESTMENT								29,414
OTHER including receivables								3,270
GAIN/ (IMPAIRMENT)								$ 19,002
SQUARE FOOTAGE unaudited | ft²								142,856
Number of properties sold | property										2	2
Gadsden, AL | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE							$ 5,500
CLOSING ADJUSTMENTS							(280)
NET PROCEEDS							5,220
NET REAL ESTATE INVESTMENT							5,914
OTHER including receivables							175
GAIN/ (IMPAIRMENT)							$ (869)
SQUARE FOOTAGE unaudited | ft²							120,192
Number of properties sold | property							3
Dallas, TX | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE	$ 800					$ 23,000
CLOSING ADJUSTMENTS	(103)					(1,117)
NET PROCEEDS	697					21,883
NET REAL ESTATE INVESTMENT	712					18,733
OTHER including receivables	167					1,966
GAIN/ (IMPAIRMENT)	$ (182)					$ 1,184
SQUARE FOOTAGE unaudited | ft²	13,818					190,160
Number of properties sold | property					4
Chicago, IL | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE				$ 13,300
CLOSING ADJUSTMENTS				(388)
NET PROCEEDS				12,912
NET REAL ESTATE INVESTMENT				23,213
OTHER including receivables				706
GAIN/ (IMPAIRMENT)				$ (11,007)
SQUARE FOOTAGE unaudited | ft²				95,436
Des Moines, IA | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE			$ 47,000
CLOSING ADJUSTMENTS			(901)
NET PROCEEDS			46,099
NET REAL ESTATE INVESTMENT			32,312
OTHER including receivables			1,037
GAIN/ (IMPAIRMENT)			$ 12,750
SQUARE FOOTAGE unaudited | ft²			132,617
Number of properties sold | property			3
Number of land parcels held for development | property			2
Aberdeen, SD | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE		$ 12,750
CLOSING ADJUSTMENTS		(299)
NET PROCEEDS		12,451
NET REAL ESTATE INVESTMENT		10,337
OTHER including receivables		0
GAIN/ (IMPAIRMENT)		$ 2,114
SQUARE FOOTAGE unaudited | ft²		58,285
Springfield MO | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE													$ 138,000
CLOSING ADJUSTMENTS													0
NET PROCEEDS													138,000
NET REAL ESTATE INVESTMENT													92,400
OTHER including receivables													3,900
GAIN/ (IMPAIRMENT)													$ 41,700
SQUARE FOOTAGE unaudited | ft²													186,000
OKLAHOMA | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE													$ 106,500
CLOSING ADJUSTMENTS													0
NET PROCEEDS													106,500
NET REAL ESTATE INVESTMENT													76,800
OTHER including receivables													3,100
GAIN/ (IMPAIRMENT)													$ 26,600
SQUARE FOOTAGE unaudited | ft²													200,000
Miami, FL | Real Estate Dispositions
Real Estate Dispositions [Line Items]
SALES PRICE												$ 5,000
CLOSING ADJUSTMENTS												(200)
NET PROCEEDS												4,800
NET REAL ESTATE INVESTMENT												2,600
OTHER including receivables												100
GAIN/ (IMPAIRMENT)												$ 2,100
SQUARE FOOTAGE unaudited | ft²												26,000
Number of properties sold | property															2