Summary of Significant Accounting Policies (Narrative) (Details)		12 Months Ended
	Nov. 25, 2020	Dec. 31, 2020 USD ($) Segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 shares	May 01, 2019 shares	Apr. 30, 2019 shares	Jan. 01, 2019 USD ($)
Summary Of Significant Accounting Policies [Line Items]
VIE real estate owned carrying value		$ 1,527,478,000	$ 1,515,206,000	$ 1,508,682,000
Mortgage loan payable		45,385,000	46,370,000
Depreciation expense		43,600,000	41,800,000	36,100,000
Cash at consolidated joint ventures		200,000	300,000
Uncollectible lease rental revenue		8,300,000	2,400,000
Deferred rent receivables written-off		1,400,000	300,000
Allowance for doubtful accounts receivable		1,400,000	600,000
Provision for doubtful accounts included in operating, maintenance and management expenses		$ 1,500,000	400,000	$ 2,200,000
Number of reportable segment | Segment		1
Operating lease, right-of-use asset		$ 13,828,000	13,638,000					$ 14,600,000
Operating lease, right-of-use liability		14,077,000						$ 14,600,000
Operating Lease, Liability, Statement of Financial Position [Extensible List]								us-gaap:AccountsPayableAndAccruedLiabilitiesMember
Operating lease cost			2,800,000
Adjustment to opening equity prior period			$ 500,000
Lease rent deferred		3,200,000
Lease rent deferrals continued to recognize rental income		2,400,000
Lease rent waived		$ 1,500,000
2017 Stock Incentive Plan [Member]
Summary Of Significant Accounting Policies [Line Items]
Maximum number of shares may be issued under the plan | shares						909,000	303,000
Maximum number of shares to be granted per year to a participant | shares					76,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Real estate investments useful life		3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Real estate investments useful life		40 years
Variable Interest Entity, Primary Beneficiary [Member] | Other Ownership Interest [Member]
Summary Of Significant Accounting Policies [Line Items]
VIE real estate owned carrying value		$ 36,900,000
Mortgage loan payable		$ 0
Variable Interest Entity, Primary Beneficiary [Member] | Crossroads II [Member] | Other Ownership Interest [Member]
Summary Of Significant Accounting Policies [Line Items]
Ownership percentage		60.00%
Variable Interest Entity, Primary Beneficiary [Member] | San Souci Plaza [Member]
Summary Of Significant Accounting Policies [Line Items]
VIE real estate owned carrying value		$ 25,400,000
Mortgage loan payable		$ 0
Common Stock [Member]
Summary Of Significant Accounting Policies [Line Items]
Stockholders' equity, reverse stock split, conversion ratio	0.15
Stockholders' equity, reverse stock split		Each 6.6 shares of the Company's issued and outstanding common stock were combined into one share of the Company's common stock.