Commitments And Contingencies (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) center partnership	Dec. 31, 2017 USD ($) partnership	Dec. 31, 2016 USD ($)
Long-term Purchase Commitment [Line Items]
Operating leases, rental expense	$ 3,100	$ 2,900	$ 3,000
Future minimum revenues under subleases	$ 22,800	27,100	$ 27,000
Capital leased assets, number of units | center	2
Capital leases, total assets	$ 15,700	16,800
Capital leases, accumulated depreciation	14,100	15,500
Capital leases, future minimum payments	29,400
Capital leases, future minimum payments, interest	7,500
Capital leases	21,898	$ 21,000
Total future minimum revenues under subleases, applicable to these capital leases	14,400
Capital Additions [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, commitment	$ 190,700
Capital Additions [Member] | Minimum [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, period (in months)	12 months
Capital Additions [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Purchase contract, period (in months)	36 months
DownREIT [Member]
Long-term Purchase Commitment [Line Items]
Number of real estate joint ventures | partnership	2	2
Aggregate redemption value	$ 36,000	$ 47,000
Debt, Net [Member]
Long-term Purchase Commitment [Line Items]
Capital leases	$ 21,900
Lessor Operating Leases [Member] | Maximum [Member]
Long-term Purchase Commitment [Line Items]
Lease term	10 years
Lease renewal term	5 years