Debt (Summary of Debt) (Details) - USD ($)	Jun. 30, 2020	Feb. 28, 2020	Feb. 27, 2020	Dec. 31, 2019
Debt Instrument
Deferred financing costs, net and other	$ (31,790,000)			$ (38,407,000)
Long term debt	$ 2,317,515,000			1,766,712,000
Mortgages
Debt Instrument
Interest rate, end of period (percent)	3.19%
Long-term debt, gross	$ 5,662,657,000			5,670,016,000
Deferred financing costs, net and other	(24,305,000)			(30,119,000)
Long term debt	$ 5,638,352,000			5,639,897,000
Mortgages | Fixed Rate
Debt Instrument
Interest rate, end of period (percent)	3.52%
Long-term debt, gross	$ 4,589,860,000			4,601,516,000
Mortgages | Variable Rate
Debt Instrument
Interest rate, end of period (percent)	1.76%
Long-term debt, gross	$ 1,072,797,000			1,068,500,000
Senior Unsecured Notes
Debt Instrument
Interest rate, end of period (percent)	3.50%
Long-term debt, gross	$ 450,000,000			450,000,000
Deferred financing costs, net and other	(3,721,000)			(4,128,000)
Long term debt	$ 446,279,000			445,872,000
Unsecured term loan
Debt Instrument
Interest rate, end of period (percent)	3.70%
Long-term debt, gross	$ 800,000,000	$ 800,000,000	$ 750,000,000	750,000,000
Deferred financing costs, net and other	(3,764,000)			(4,160,000)
Long term debt	$ 796,236,000			745,840,000
Unsecured Revolving Credit Facilities
Debt Instrument
Interest rate, end of period (percent)	1.09%
Long term debt	$ 1,075,000,000			$ 575,000,000