Revenues (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Lessor Lease Description [Line Items]
Total revenues	$ 127,550,000	$ 135,538,000	$ 144,083,000
Unpaid billed charges of rent and tenant reimbursements	700,000	6,900,000
Unrecorded revenue from tenants	700,000	6,900,000
Expense recoveries	$ 32,500,000	31,100,000	$ 34,400,000
Other Income [Member] | Contract Termination [Member]
Lessor Lease Description [Line Items]
Total revenues		$ 7,100,000