Multifamily Developmental Activity (Narrative) (Details) $ in Thousands	1 Months Ended	9 Months Ended
	Aug. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) property	Dec. 31, 2019 USD ($)
Real Estate Facilities [Line Items]
Land cost basis		$ 3,069,340	$ 3,047,727
Brentford at The Mile [Member]
Real Estate Facilities [Line Items]
Number of Units in Multi-Family Asset | property		411
Value of property contributed	$ 18,500
Land cost basis	$ 5,400	$ 5,400
Development cost incurred, inclusive of land cost		5,500
Demolition costs		$ 300
Brentford at The Mile [Member] | Investment in Joint Venture [Member]
Real Estate Facilities [Line Items]
Economic interest in joint venture, percentage		98.20%
Brentford at The Mile [Member] | JV Partner [Member]
Real Estate Facilities [Line Items]
Economic interest in joint venture, percentage		1.80%
Minimum [Member] | Brentford at The Mile [Member]
Real Estate Facilities [Line Items]
Period to complete construction	24 months
Estimated development costs	$ 110,000
Maximum [Member] | Brentford at The Mile [Member]
Real Estate Facilities [Line Items]
Period to complete construction	36 months
Development costs incurred	$ 115,000