CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Accumulated Deficit	Total
Balance as of beginning of period at Dec. 31, 2018	$ 34	$ 306,053		$ (201,109)	$ 104,978
Balance as of beginning of period (in shares) at Dec. 31, 2018	33,863,077
Stockholders' Equity
At the market offering, net of offering costs	$ 2	8,423			8,425
At the market offering, net of offering costs (in shares)	2,074,799
Exercise of stock options		42			42
Exercise of stock options (in shares)	24,714
Issuance under employee stock purchase plan		545			545
Issuance under employee stock purchase plan (in shares)	123,664
Stock-based compensation expense		10,049			10,049
Net loss				(94,347)	(94,347)
Balance as of end of period at Dec. 31, 2019	$ 36	325,112		(295,456)	29,692
Balance as of end of period (in shares) at Dec. 31, 2019	36,086,254
Stockholders' Equity
At the market offering, net of offering costs	$ 5	33,129			33,134
At the market offering, net of offering costs (in shares)	5,173,730
Exercise of stock options	$ 1	1,086			1,087
Exercise of stock options (in shares)	345,479
Issuance under employee stock purchase plan		1,016			1,016
Issuance under employee stock purchase plan (in shares)	314,397
Common stock offering, net of offering costs	$ 17	125,406			125,423
Common stock offering, net of offering costs (in shares)	16,979,371
Stock-based compensation expense		13,966			13,966
Warrant exercises (in shares)	16,144
Change in fair value of investments			$ 4		4
Net loss				(104,327)	(104,327)
Balance as of end of period at Dec. 31, 2020	$ 59	$ 499,715	$ 4	$ (399,783)	$ 99,995
Balance as of end of period (in shares) at Dec. 31, 2020	58,915,375