CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue from Contract with Customer, Product and Service [Extensible List]			us-gaap:LicenseMember
Collaboration revenue – related party	$ 2,435	$ 1,784	$ 8,592	$ 7,066
Operating expenses:
Research and development	11,804	7,945	27,696	20,447
General and administrative	2,470	1,366	5,816	4,062
Expense from operations	14,274	9,311	33,512	24,509
Loss from operations	(11,839)	(7,527)	(24,920)	(17,443)
Other income (expense):
Interest income	86	279	474	902
Other	(76)	(31)	(145)	(72)
Total other income	10	248	329	830
Net loss	(11,829)	(7,279)	(24,591)	(16,613)
Unrealized gain (loss) on short-term investments	(28)	10	(64)	119
Comprehensive loss	$ (11,857)	$ (7,269)	$ (24,655)	$ (16,494)
Net loss per share – basic and diluted (in dollars per share)	$ (1.54)	$ (0.96)	$ (3.21)	$ (2.20)
Weighted-average common shares outstanding (in shares)	7,700,371	7,572,746	7,656,077	7,543,831