Significant Acquisitions and Dispositions Dispositions (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) buildings	Dec. 31, 2019 USD ($) buildings	Dec. 31, 2018 USD ($) buildings
Dispositions Disclosures [Line Items]
Proceeds from Sale of Real Estate Held-for-investment		$ 336,255	$ 432,662	$ 511,391
Proceeds from Collection of Notes Receivable		$ 110,000
Number of Real Estate Properties Sold	18	7	28	15
Proceeds from Sale of Productive Assets	$ 217,500
Gain (Loss) on Sale of Properties	$ 146,300	$ 138,269	$ 242,543	$ 219,114
Square Feet of Properties Sold	4,100,000