Supplemental Disclosures for the Statement of Consolidated Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Supplemental Cash Flow Elements [Abstract]
Accrued capital expenditures and deferred lease costs	$ 24,035	$ 29,828
Change in accrued dividends and discount on dividend reinvestments	(26,427)	(26,972)
Change in accrued share repurchases as part of an announced plan	0	(4,417)
Accrued deferred financing costs	130	0
Accrued stock issuance costs	0	441
Cash and cash equivalents	23,958	10,284	$ 13,545	$ 4,571
Restricted cash and escrows	1,781	1,820	1,841	1,463
Total cash, cash equivalents, and restricted cash and escrows shown in the consolidated statement of cash flows	$ 25,739	$ 12,104	$ 15,386	$ 6,034