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	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Total operating expenses	(2,371)	(2,271)	(3,506)	(2,412)	(2,831)	(2,521)	(2,596)	(3,214)	(10,560)	(11,162)	(9,698)
Total other income	(2,326)	(142)	(7,287)	(360)	(8,116)	(2,850)	(209)	(1,037)	(10,115)	(12,212)	(1,493)
(Loss) income from continuing operations	(45)	(2,129)	3,781	(2,052)	5,285	329	(2,387)	(2,177)	(445)	1,050	(8,205)
(Loss) income from discontinued operations	10,636	1,984	304	(414)	(1,672)	(1,898)	(2,064)	(2,253)	12,510	(7,887)	(10,027)
Net income (loss)	10,591	(145)	4,085	(2,466)	3,613	(1,569)	(4,451)	(4,430)	12,065	(6,837)	(18,232)
Net income (loss) attributable to common shareholders	$ 10,591	$ (145)	$ 4,085	$ (2,466)	$ 3,613	$ (1,569)	$ (4,451)	$ (4,430)	$ 12,065	$ (6,837)	$ (18,317)
Net (loss) income per common share - basic and diluted (in dollars per share)	$ 0.06	$ 0.00	$ 0.02	$ (0.01)	$ 0.02	$ (0.01)	$ (0.03)	$ (0.03)	$ 0.07	$ (0.04)	$ (0.11)
Weighted-average shares outstanding (in shares)	177,997	177,979	177,591	177,076	176,912	176,456	176,183	175,565	177,663	176,283	169,270