SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) - Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 14,865	$ 12,548	$ 7,001	$ 5,963	$ 3,208	$ 2,429	$ 790	$ 93	$ 40,377	$ 6,520	$ 0
Total operating expenses	(16,420)	(14,108)	(8,808)	(7,693)	(5,377)	(4,419)	(2,905)	(1,375)	(47,029)	(14,076)	(1,223)
Total other expenses	(3,159)	(2,776)	(1,154)	(1,201)	(849)	(894)	(324)	(183)
Total expense support from the Advisor	(6,966)	658	1,045	(2,205)	1,767	1,354	1,400	1,062	(7,468)	5,583	1,735
Net loss	(11,680)	(3,678)	(1,916)	(5,136)	(1,251)	(1,530)	(1,039)	(403)	(22,410)	(4,223)	203
Net loss attributable to common stockholders	$ (11,662)	$ (3,672)	$ (1,912)	$ (5,122)	$ (1,251)	$ (1,530)	$ (1,039)	$ (403)	$ (22,368)	$ (4,223)	$ 203
Net loss per common share - basic and diluted (in dollars per share)	$ (0.25)	$ (0.09)	$ (0.06)	$ (0.20)	$ (0.08)	$ (0.15)	$ (0.17)	$ (0.14)	$ (0.60)	$ (0.46)	$ 0.53
Weighted-average shares outstanding (in shares)	46,989	41,808	34,452	25,997	16,562	10,491	6,248	2,961	37,382	9,107	381