Condensed Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (18,839)	$ (10,676)	$ (36,463)	$ (18,146)
Other comprehensive income:
Unrealized gain on investments	91		253
Comprehensive loss	$ (18,748)	$ (10,676)	$ (36,210)	$ (18,146)