STOCK-BASED COMPENSATION - Stock Option Activity (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Shares
Options outstanding (in shares) | shares	1,793,602
Acquired under Vical Plan (in shares) | shares	184,087
Granted (in shares) | shares	1,088,260
Exercised (in shares) | shares	0
Forfeited (in shares) | shares	(175,587)
Options outstanding (in shares) | shares	696,842
Weighted Average Exercise Price
Weighted Average Exercise Price (in usd per share) | $ / shares	$ 13.21
Weighted Average Exercise Price, Acquired under Vical Plan (in usd per share) | $ / shares	75.98
Weighted Average Exercise Price, Granted (in usd per share) | $ / shares	4.67
Weighted Average Exercise Price, Exercised (in usd per share) | $ / shares	0
Weighted Average Exercise Price, Forfeited or expired (in usd per share) | $ / shares	28.22
Weighted Average Exercise Price (in usd per share) | $ / shares	$ 13.00
Total Intrinsic Value
Intrinsic Value, Outstanding | $	$ 4,971
Intrinsic Value, Options vested and exercisable | $	$ 73,878
Weighted Average Remaining Contractual Life (In Years)
Weighted Average Remaining Contractual Life (In Years), Outstanding	8 years 5 months 26 days
Weighted Average Remaining Contractual Life (In Years), Options vested and exercisable	5 years 11 months 19 days
Options vested and exercisable (in shares) | shares	525,665
Options vested and exercisable (in usd per share) | $ / shares	$ 28.41