ORGANIZATION, BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details)			3 Months Ended		6 Months Ended
	Apr. 14, 2020 USD ($)	Feb. 05, 2020 shares	Jun. 30, 2020 USD ($) shares	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) shares	Jun. 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	80,000,000
Accumulated deficit			$ (558,643,000)		$ (558,643,000)					$ (533,025,000)
Revenues			0	$ 1,391,000	0	$ 1,907,000
Accrued expenses and other current liabilities			7,108,000		7,108,000					$ 9,770,000
Gain on dispositions, net			3,761,000	0	3,761,000	0
Grant from CPRIT
Class of Stock [Line Items]
Restricted cash, noncurrent			100,000		100,000						$ 4,200,000
Release Of Restricted Cash					(3,300,000)
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]
Escrow Deposits Related to Property Sales	$ 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			3,800,000		3,800,000
Grants
Class of Stock [Line Items]
Revenues			0	$ 1,391,000	0	$ 1,907,000
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		0
Accrued expenses and other current liabilities			$ 800,000		$ 800,000