Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Common Stock
Period Start Balance	$ 209,357	$ 94,026
Balance (in shares)	39,603,771
Shares issued under stock option and employee stock purchase plans	$ 74	24
Shares issued in connection with at the market agreement		1,614
Stock-based compensation	1,275	686
Unrealized loss on marketable securities	(2)	(22)
Net loss	(16,538)	(12,625)
Period End Balance	$ 194,166	83,703
Balance (in shares)	39,614,638
Net proceeds from sale of common stock		1,613
Common Stock
Common Stock
Period Start Balance	$ 40	$ 17
Balance (in shares)	39,603,771	16,972,077
Shares issued under stock option and employee stock purchase plans (in shares)	10,867	12,573
Shares issued in connection with at the market agreement		$ 1
Shares issued in connection with at the market agreement (in shares)		746,152
Period End Balance	$ 40	$ 18
Balance (in shares)	39,614,638	17,730,802
Aggregate gross offering price available	$ 50,000
Additional Paid-In Capital
Common Stock
Period Start Balance	1,279,824	$ 1,104,706
Shares issued under stock option and employee stock purchase plans	74	24
Shares issued in connection with at the market agreement		1,613
Stock-based compensation	1,275	686
Period End Balance	1,281,173	1,107,029
Accumulated Other Comprehensive Income
Common Stock
Period Start Balance	2,589	2,619
Unrealized loss on marketable securities	(2)	(22)
Period End Balance	2,587	2,597
Accumulated Deficit
Common Stock
Period Start Balance	(1,073,096)	(1,013,316)
Net loss	(16,538)	(12,625)
Period End Balance	$ (1,089,634)	$ (1,025,941)