Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating expenses:
Research and development	$ 15,174,000	$ 15,464,000	$ 32,593,000	$ 31,141,000
General and administrative	5,071,000	5,923,000	10,913,000	11,050,000
Total operating expenses	20,245,000	21,387,000	43,506,000	42,191,000
Loss from operations	(20,245,000)	(21,387,000)	(43,506,000)	(42,191,000)
Other (expense) income:
Interest (expense) income, net	(458,000)	446,000	(639,000)	951,000
Other income, net	140,000	0	606,000	0
Other (expense) income, net	(318,000)	446,000	(33,000)	951,000
Loss before income taxes	(20,563,000)	(20,941,000)	(43,539,000)	(41,240,000)
Income tax expense	(89,000)	0	(154,000)	0
Net loss	$ (20,652,000)	$ (20,941,000)	$ (43,693,000)	$ (41,240,000)
Net loss per share attributable to common stockholders, basic and diluted (in dollars per share)	$ (0.63)	$ (0.65)	$ (1.35)	$ (1.29)
Weighted-average number of common shares outstanding, basic and diluted (in shares)	32,634,468	32,041,401	32,442,259	31,983,558
Comprehensive loss:
Net loss	$ (20,652,000)	$ (20,941,000)	$ (43,693,000)	$ (41,240,000)
Other comprehensive loss:
Unrealized gain (loss) on investments, net of tax of $0	0	3,000	0	19,000
Comprehensive loss	(20,652,000)	(20,938,000)	(43,693,000)	(41,221,000)
Tax portion of unrealized loss on investments	$ 0	$ 0	$ 0	$ 0