Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Total revenues	$ 1,402	$ 1,438	$ 2,643	$ 3,794
Operating expenses:
Research and development	8,578	13,827	17,527	27,342
General and administrative	3,110	6,312	6,315	13,998
Total operating expenses	11,688	20,139	23,842	41,340
Loss from operations	(10,286)	(18,701)	(21,199)	(37,546)
Other income:
Interest income and other, net	270	1,051	763	2,203
Net loss	(10,016)	(17,650)	(20,436)	(35,343)
Other comprehensive loss:
Unrealized gain on debt investments, net	141	77	95	217
Comprehensive loss	$ (9,875)	$ (17,573)	$ (20,341)	$ (35,126)
Per share information:
Net loss, basic and diluted (in dollars per share)	$ (0.16)	$ (0.35)	$ (0.33)	$ (0.69)
Weighted-average shares outstanding, basic and diluted (in shares)	62,042,778	51,130,104	61,892,407	51,009,935
Contract revenue
Total revenues	$ 1,396	$ 1,438	$ 2,567	$ 3,794
Licensing revenue
Total revenues	$ 6	$ 0	$ 76	$ 0