Schedule II Valuation and qualifying accounts (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Allowance for doubtful accounts - Tenant rent receivables
Movement in valuation and qualifying accounts
Balance at beginning of year	$ 505,000	$ 300,000	$ 200,000
Additions (Decreases) charged to costs and expenses	157,000	340,000	213,000
Deductions	(129,000)	(135,000)	(113,000)
Balance at end of year	$ 533,000	505,000	300,000
Allowance for doubtful accounts - Straight-line rent receivable
Movement in valuation and qualifying accounts
Balance at beginning of year		50,000	50,000
Deductions		$ (50,000)
Balance at end of year			$ 50,000