Stockholders' Equity (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				6 Months Ended
	Jul. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Common Stock
Balance	$ 182,282	$ 194,166	$ 209,357	$ 83,703	$ 94,026	$ 209,357	$ 94,026
Balance (in shares)	39,616,696		39,603,771			39,603,771
Shares issued under stock option and employee stock purchase plans		(25)	$ (74)		(24)
Shares issued in connection with at the market agreement				23,692	1,614
Shares issued in underwritten offering				141,361
Stock-based compensation		1,509	1,275	722	686
Unrealized gain (loss) on marketable securities		5	(2)	(3)	(22)	$ 3	(25)
Net loss		(13,373)	(16,538)	(11,031)	(12,625)	(29,911)	(23,656)
Balance		$ 182,282	194,166	238,444	83,703	$ 182,282	238,444
Balance (in shares)		39,616,696				39,616,696
Aggregate gross offering price available		$ 50,000				$ 50,000
Net proceeds from sale of common stock							166,667
Underwritten Public Offering
Common Stock
Common stock issued (in shares)	6,845,238
Net proceeds from sale of common stock	$ 270,000
Common Stock
Common Stock
Balance	$ 40	$ 40	$ 40	$ 18	$ 17	$ 40	$ 17
Balance (in shares)	39,616,696	39,614,638	39,603,771	17,730,802	16,972,077	39,603,771	16,972,077
Shares issued under stock option and employee stock purchase plans (in shares)		2,058	10,867		12,573
Shares issued in connection with at the market agreement				$ 6	$ 1
Shares issued in connection with at the market agreement (in shares)				5,978,452	746,152
Shares issued in underwritten offering				$ 15
Shares issued in underwritten offering (in shares)				15,384,614
Balance		$ 40	$ 40	$ 39	$ 18	$ 40	$ 39
Balance (in shares)		39,616,696	39,614,638	39,093,868	17,730,802	39,616,696	39,093,868
Additional Paid-In Capital
Common Stock
Balance	$ 1,282,657	$ 1,281,173	$ 1,279,824	$ 1,107,029	$ 1,104,706	$ 1,279,824	$ 1,104,706
Shares issued under stock option and employee stock purchase plans		(25)	(74)		(24)
Shares issued in connection with at the market agreement				23,686	1,613
Shares issued in underwritten offering				141,346
Stock-based compensation		1,509	1,275	722	686
Balance		1,282,657	1,281,173	1,272,783	1,107,029	1,282,657	1,272,783
Accumulated Other Comprehensive Income
Common Stock
Balance	2,592	2,587	2,589	2,597	2,619	2,589	2,619
Unrealized gain (loss) on marketable securities		5	(2)	(3)	(22)
Balance		2,592	2,587	2,594	2,597	2,592	2,594
Accumulated Deficit
Common Stock
Balance	$ (1,103,007)	(1,089,634)	(1,073,096)	(1,025,941)	(1,013,316)	(1,073,096)	(1,013,316)
Net loss		(13,373)	(16,538)	(11,031)	(12,625)
Balance		$ (1,103,007)	$ (1,089,634)	$ (1,036,972)	$ (1,025,941)	$ (1,103,007)	$ (1,036,972)