Organization and Summary of Significant Accounting Policies (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) Tenant	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) Tenant	Sep. 30, 2020 USD ($)	Jun. 30, 2021 USD ($)	May 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Accounting Policies [Line Items]
Interest costs capitalized	$ 87,000	$ 332,000	$ 215,000	$ 1,218,000
Percentage of total properties for which revenue recognized on cash basis	6.00%		6.00%
Percentage of aggregate gross leasable area for which revenue recognized on cash basis	7.00%		7.00%
Percentage of tenants for which revenue recognized on cash basis | Tenant	11		11
Revenue recognized on cash basis	$ 13,630,000	$ 726,000	$ 37,999,000	$ 930,000
Mortgage loan
Accounting Policies [Line Items]
Mortgage receivable	2,117,000		2,117,000				$ 2,482,000
Allowance for credit loss	135,000		$ 135,000				158,000
Collectability analysis, period used			15 years
Minimum
Accounting Policies [Line Items]
Initial lease term			10 years
Maximum
Accounting Policies [Line Items]
Initial lease term			20 years
Line of Credit
Accounting Policies [Line Items]
Revolving credit facility borrowing capacity	1,100,000,000		$ 1,100,000,000		$ 1,100,000,000	$ 900,000,000
Notes Payable to Banks
Accounting Policies [Line Items]
Debt costs	38,145,000		38,145,000				31,140,000
Debt costs accumulated amortization	$ 8,670,000		$ 8,670,000				$ 9,317,000