ORGANIZATION, BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)				3 Months Ended		9 Months Ended
	Sep. 15, 2020 USD ($)	Apr. 14, 2020 USD ($)	Feb. 05, 2020 shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) shares	Sep. 30, 2019 USD ($)	Jun. 15, 2020 shares	Jun. 14, 2020 shares	Feb. 04, 2020 shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2017 USD ($)	Aug. 09, 2017 USD ($)
Class of Stock [Line Items]
Reverse stock split ratio			0.1
Common stock, authorized (in shares) | shares			40,000,000	80,000,000		80,000,000		80,000,000	40,000,000	200,000,000	40,000,000
Accumulated deficit				$ (559,530,000)		$ (559,530,000)					$ (533,025,000)
Revenues				0	$ 103,000	0	$ 2,010,000
Accrued expenses and other current liabilities				6,677,000		6,677,000					$ 9,770,000
Gain on dispositions, net				0	0	3,761,000	0
Held in escrow
Class of Stock [Line Items]
Restricted cash, noncurrent				1,100,000		1,100,000
2130 W. Holcombe Blvd.
Class of Stock [Line Items]
Cash proceeds subject to escrow provisions		$ 1,500,000
Amount paid upon closing of asset sale		$ 15,000,000.0
Disposal Group, Held-for-sale, Not Discontinued Operations
Class of Stock [Line Items]
Assets held for sale, property and equipment				12,000,000.0		12,000,000.0
Assets held for sale, right-of-use assets				4,800,000		4,800,000
Assets held for sale, current lease liabilities				1,400,000		1,400,000
Assets held for sale, long-term lease liabilities				4,600,000		4,600,000
Gain on dispositions, net	$ 1,100,000			3,800,000		3,800,000
Grants
Class of Stock [Line Items]
Revenues				0	103,000	0	2,010,000
CPRIT
Class of Stock [Line Items]
Grants awarded													$ 16,900,000
Advanced funding												$ 4,200,000
CPRIT | Grants
Class of Stock [Line Items]
Revenues				0	$ 100,000	0	$ 2,000,000.0
Accrued expenses and other current liabilities				$ 800,000		$ 800,000