Debt And Lines Of Credit , Schedule of debt and lines of credit (Details) - USD ($)		3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 28, 2021	Jun. 30, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Document Period End Date		Jun. 30, 2021
Secured debt		$ 3,457,734,000			$ 3,457,734,000		$ 3,489,983,000
Unsecured Debt		$ 853,441,000			$ 853,441,000		$ 1,267,093,000
Debt weighted average to maturity, years					10 years 4 months 24 days		9 years 4 months 24 days
Weighted average interest rate		3.519%			3.519%		3.37%
Mortgage Term Loans		$ 3,418,097,000			$ 3,418,097,000		$ 3,444,967,000
Loans Pledged as Collateral		39,637,000			39,637,000		45,016,000
Line of credit and other							1,197,181,000
Total debt		4,311,175,000			4,311,175,000		4,757,076,000
Gain (Loss) on Extinguishment of Debt		(8,108,000)	$ (1,930,000)		(8,108,000)	$ (5,209,000)
Collateralized term loans - CMBS [Member]
Debt Instrument [Line Items]
Secured debt		$ 1,146,146,000			$ 1,146,146,000		$ 267,205,000
Debt weighted average to maturity, years					8 years 7 months 6 days		2 years 10 months 24 days
Weighted average interest rate		3.226%			3.226%		4.789%
Secured borrowing [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 230,000,000			$ 268,800,000
Secured debt		$ 3,400,000,000			$ 3,400,000,000
Debt instrument term				15 years			12 years
Debt Instrument, Interest Rate, Stated Percentage				2.995%			2.662%
Preferred OP units [Member]
Debt Instrument [Line Items]
Secured debt		34,663,000			34,663,000
Preferred OP units - mandatorily redeemable							$ 34,663,000
Debt weighted average to maturity, years							5 years 1 month 6 days
Weighted average interest rate							5.932%
Preferred Equity, Mandatorily Redeemable [Member]
Debt Instrument [Line Items]
Preferred OP units - mandatorily redeemable		$ 35,249,000			$ 35,249,000		$ 35,249,000
Debt instrument term					3 years 3 months 18 days
Debt weighted average to maturity, years							3 years 9 months 18 days
Weighted average interest rate		6.00%			6.00%		6.00%
Senior Unsecured NOtes
Debt Instrument [Line Items]
Debt instrument, face amount	$ 600,000,000.0
Unsecured Debt		$ 591,688,000			$ 591,688,000		$ 0
Debt instrument term	10 years
Debt Instrument, Interest Rate, Stated Percentage	2.70%
Debt weighted average to maturity, years					10 years		0 years
Weighted average interest rate		2.70%			2.70%		0.00%
Senior Unsecured Notes1
Debt Instrument [Line Items]
Unsecured Debt		$ 591,700,000			$ 591,700,000
Matures December 1, 2021, 5.98 Percent Interest Rate | Secured borrowing [Member]
Debt Instrument [Line Items]
Reduction in secured borrowing balance			$ 52,710,000		0
Interest rate			5.98%			5.98%
Gain (Loss) on Extinguishment of Debt			$ 1,930,000
Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Debt Instrument [Line Items]
Secured debt		$ 365,402,000			$ 365,402,000		$ 1,150,924,000
Debt weighted average to maturity, years					3 years 4 months 24 days		9 years 1 month 6 days
Weighted average interest rate		3.853%			3.853%		3.23%
Life Companies [Member] | Collateralized Mortgage Backed Securities [Member]
Debt Instrument [Line Items]
Secured debt		$ 1,642,185,000			$ 1,642,185,000		$ 1,658,239,000
Debt weighted average to maturity, years					15 years 9 months 18 days		16 years 3 months 18 days
Weighted average interest rate		3.991%			3.991%		3.99%
Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Debt Instrument [Line Items]
Secured debt		$ 264,364,000			$ 264,364,000		$ 368,599,000
Debt weighted average to maturity, years					2 years 4 months 24 days		3 years 10 months 24 days
Weighted average interest rate		4.789%			4.789%		3.854%
Collateralized Term Loan
Debt Instrument [Line Items]
Debt weighted average to maturity, years					2 years 3 months 18 days		2 years 9 months 18 days
Weighted average interest rate		1.30%			1.30%		1.31%
Reported Value Measurement
Debt Instrument [Line Items]
Secured debt		$ 3,457,734,000			$ 3,457,734,000		$ 3,489,983,000
Unsecured Debt		$ 853,441,000			$ 853,441,000		$ 1,267,093,000
Reported Value Measurement | Secured borrowing [Member]
Debt Instrument [Line Items]
Debt weighted average to maturity, years					4 years 7 months 6 days
Weighted average interest rate		5.932%			5.932%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit and other		$ 191,841,000			$ 191,841,000
Revolving Credit Facility [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Debt weighted average to maturity, years					3 years 10 months 24 days		3 years 8 months 12 days
Weighted average interest rate		0.928%			0.928%		2.107%