Noncontrolling Interests (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Noncontrolling Interests [Line Items]
Common units in operating partnership			7,305,355
Noncontrolling interests	$ 219,463		$ 219,463		$ 216,135
Capital contribution to joint venture	$ 438		$ 438
Number of shares of common stock for each unit of limited partnership interest redeemed	1		1
Net income allocation to noncontrolling interests - common units	$ 8,128	$ 7,006	$ 25,985	$ 21,643
Net (income) loss allocated to Noncontrolling interest - joint venture	(4)	14	26	27
Distribution paid			109	78
PS [Member]
Noncontrolling Interests [Line Items]
Noncontrolling interests	216,200		216,200		$ 213,200
JV Partner [Member]
Noncontrolling Interests [Line Items]
Noncontrolling interests	$ 3,300	$ 2,900	$ 3,300	$ 2,900
Brentford at The Mile [Member] | JV Partner [Member]
Noncontrolling Interests [Line Items]
Consolidated entity ownership percentage	1.80%		1.80%