Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	2018 ATM	Public Stock Offering	2020 ATM	Common Stock	Common Stock 2018 ATM	Common Stock Public Stock Offering	Common Stock 2020 ATM	Additional Paid-in Capital	Additional Paid-in Capital 2018 ATM	Additional Paid-in Capital Public Stock Offering	Additional Paid-in Capital 2020 ATM	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balance at beginning of period (in shares) at Dec. 31, 2019					45,388,023
Balance at beginning of period at Dec. 31, 2019	$ 78,318				$ 5				$ 270,662				$ 25	$ (192,374)
Increase (Decrease) in Stockholders' Equity
Exercise of common stock warrant in exchange for common stock (in shares)					2,574,971
Exercise of stock options (in shares)					43,055
Exercise of stock options	119								119
Stock-based compensation expense	1,609								1,609
Other comprehensive income (loss)	(29)												(29)
Net (loss) income	(16,926)													(16,926)
Balance at end of period (in shares) at Mar. 31, 2020					48,006,049
Balance at end of period at Mar. 31, 2020	63,091				$ 5				272,390				(4)	(209,300)
Balance at beginning of period (in shares) at Dec. 31, 2019					45,388,023
Balance at beginning of period at Dec. 31, 2019	78,318				$ 5				270,662				25	(192,374)
Increase (Decrease) in Stockholders' Equity
Net (loss) income	(59,203)
Balance at end of period (in shares) at Sep. 30, 2020					68,470,081
Balance at end of period at Sep. 30, 2020	253,308				$ 7				504,876				0	(251,575)
Balance at beginning of period (in shares) at Mar. 31, 2020					48,006,049
Balance at beginning of period at Mar. 31, 2020	63,091				$ 5				272,390				(4)	(209,300)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)					206,143
Exercise of stock options	1,296								1,296
Stock-based compensation expense	1,656								1,656
Other comprehensive income (loss)	6												6
Net (loss) income	(19,786)													(19,786)
Issuance of common stock under public offering, net of issuance costs (in shares)						10,900,599	9,200,000
Issuance of common stock under public offering, net of issuance costs		$ 62,977	$ 163,991			$ 1	$ 1			$ 62,976	$ 163,990
Purchase of common stock under ESPP (in shares)					68,419
Purchase of common stock under ESPP	333								333
Balance at end of period (in shares) at Jun. 30, 2020					68,381,210
Balance at end of period at Jun. 30, 2020	273,564				$ 7				502,641				2	(229,086)
Increase (Decrease) in Stockholders' Equity
Stock issuance costs		$ 2,176	$ 10,809
Exercise of stock options (in shares)					88,871
Exercise of stock options	317								317
Stock-based compensation expense	1,918								1,918
Other comprehensive income (loss)	(2)												(2)
Net (loss) income	(22,489)													(22,489)
Balance at end of period (in shares) at Sep. 30, 2020					68,470,081
Balance at end of period at Sep. 30, 2020	253,308				$ 7				504,876				0	(251,575)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)					359,359
Exercise of stock options	1,406								1,406
Stock-based compensation expense	1,989								1,989
Net (loss) income	(28,844)													(28,844)
Purchase of common stock under ESPP (in shares)					11,848
Purchase of common stock under ESPP	228								228
Balance at end of period (in shares) at Dec. 31, 2020					68,841,288
Balance at end of period at Dec. 31, 2020	228,087				$ 7				508,499				0	(280,419)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)					148,472
Exercise of stock options	764								764
Vesting of restricted stock units, net of employee tax obligations (in shares)					61,678
Vesting of restricted stock units, net of employee tax obligations	(259)								(259)
Stock-based compensation expense	4,039								4,039
Net (loss) income	(34,693)													(34,693)
Balance at end of period (in shares) at Mar. 31, 2021					69,051,438
Balance at end of period at Mar. 31, 2021	197,938				$ 7				513,043				0	(315,112)
Balance at beginning of period (in shares) at Dec. 31, 2020					68,841,288
Balance at beginning of period at Dec. 31, 2020	$ 228,087				$ 7				508,499				0	(280,419)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)	331,141
Net (loss) income	$ (121,077)
Issuance of common stock under public offering, net of issuance costs (in shares)				2,271,074
Balance at end of period (in shares) at Sep. 30, 2021					71,865,399
Balance at end of period at Sep. 30, 2021	155,549				$ 7				557,038				0	(401,496)
Balance at beginning of period (in shares) at Mar. 31, 2021					69,051,438
Balance at beginning of period at Mar. 31, 2021	197,938				$ 7				513,043				0	(315,112)
Increase (Decrease) in Stockholders' Equity
Exercise of stock options (in shares)					42,506
Exercise of stock options	202								202
Stock-based compensation expense	4,582								4,582
Net (loss) income	(40,913)													(40,913)
Issuance of common stock under public offering, net of issuance costs (in shares)								2,271,074
Issuance of common stock under public offering, net of issuance costs				$ 33,287								$ 33,287
Purchase of common stock under ESPP (in shares)					36,198
Purchase of common stock under ESPP	417								417
Balance at end of period (in shares) at Jun. 30, 2021					71,401,216
Balance at end of period at Jun. 30, 2021	195,513				$ 7				551,531				0	(356,025)
Increase (Decrease) in Stockholders' Equity
Stock issuance costs				$ 746
Exercise of stock options (in shares)					137,301
Exercise of stock options	579								579
Vesting of restricted stock units, net of employee tax obligations (in shares)					326,882
Vesting of restricted stock units, net of employee tax obligations	0								0
Stock-based compensation expense	4,928								4,928
Net (loss) income	(45,471)													(45,471)
Balance at end of period (in shares) at Sep. 30, 2021					71,865,399
Balance at end of period at Sep. 30, 2021	$ 155,549				$ 7				$ 557,038				$ 0	$ (401,496)