Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Total revenues	$ 1,517	$ 1,517	$ 2,108
Type of revenue [extensible list]	us-gaap:LicenseMember	us-gaap:LicenseMember	us-gaap:LicenseMember
Operating expenses:
Research and development	$ 42,994	$ 60,106	$ 48,201
General and administrative	16,062	17,287	15,861
Total operating expenses	59,056	77,393	64,062
Loss from operations	(57,539)	(75,876)	(61,954)
Other income (expense):
Interest income (expense), net	1,571	1,942	1,421
Other (expense) income, net	(79)	(27)	(269)
Total other income (expense)	1,492	1,915	1,152
Net loss	(56,047)	(73,961)	(60,802)
Net loss attributable to common stockholders	$ (56,047)	$ (73,961)	$ (60,802)
Net loss per share attributable to common stockholders—basic and diluted	$ (1.84)	$ (2.92)	$ (2.90)
Weighted-average common shares outstanding—basic and diluted	30,490,783	25,371,511	20,997,211