Supplemental Disclosures for the Statement of Consolidated Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Accrued capital expenditures and deferred lease costs	$ 10,854	$ 11,276	$ 14,427
Change in accrued dividends and discount on dividend reinvestments	(74,828)	71,267	30,532
Change in accrued share repurchases as part of an announced plan	3,140	1,276	0
Investment in consolidated joint venture	0	63,026	0
Cash and cash equivalents	4,571	7,382	6,992	$ 5,441
Restricted cash and escrows	1,463	1,373	1,212	5,174
Total cash, cash equivalents, and restricted cash and escrows shown in the consolidated statement of cash flows	$ 6,034	$ 8,755	$ 8,204	$ 10,615