Statements of Operations (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement Parentheticals [Abstract]
property management fees paid to related party	$ 10,307,000	$ 8,976,000	$ 6,417,000
acquisition fees paid to related party	$ 18,054,000	$ 16,276,000	$ 12,329,000