Supplemental Disclosures for the Statement of Consolidated Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Accrued capital expenditures and deferred lease costs	$ 29,828	$ 21,784
Change in accrued dividends and discount on dividend reinvestments	(26,972)	(101,794)
Change in accrued share repurchases as part of an announced plan	(4,417)	(1,277)
Accrued stock issuance costs	441	0
Cash and cash equivalents	10,284	6,807	$ 4,571	$ 7,382
Restricted cash and escrows	1,820	1,374	1,463	1,373
Total cash, cash equivalents, and restricted cash and escrows shown in the consolidated statement of cash flows	$ 12,104	$ 8,181	$ 6,034	$ 8,755