CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	Follow-on Offering [Member]	ATM	Common Stock	Common Stock Follow-on Offering [Member]	Common Stock ATM	Additional Paid-in Capital	Additional Paid-in Capital Follow-on Offering [Member]	Additional Paid-in Capital ATM	Accumulated Other Comprehensive Gain (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ 258,507			$ 4			$ 457,994			$ 183	$ (199,674)
Beginning balance, Shares at Dec. 31, 2019				45,116,742
Vesting of common stock from option exercises	12						12
Vesting of common stock from option exercises, Shares				15,542
Issuance of common stock from option exercises	135						135
Issuance of common stock from option exercises, Shares				34,311
Issuance of common stock pursuant to employee stock purchase plan	537						537
Issuance of common stock pursuant to employee stock purchase plan, Shares				39,471
Stock-based compensation	2,883						2,883
Other comprehensive gain (loss)	(202)									(202)
Net loss	(35,331)										(35,331)
Ending balance at Mar. 31, 2020	226,541			$ 4			461,561			(19)	(235,005)
Ending balance, Shares at Mar. 31, 2020				45,206,066
Beginning balance at Dec. 31, 2019	258,507			$ 4			457,994			183	(199,674)
Beginning balance, Shares at Dec. 31, 2019				45,116,742
Other comprehensive gain (loss)	(183)
Net loss	(98,903)
Ending balance at Sep. 30, 2020	170,222			$ 4			468,795				(298,577)
Ending balance, Shares at Sep. 30, 2020				45,259,747
Beginning balance at Mar. 31, 2020	226,541			$ 4			461,561			(19)	(235,005)
Beginning balance, Shares at Mar. 31, 2020				45,206,066
Vesting of common stock from option exercises	4						4
Vesting of common stock from option exercises, Shares				1,011
Issuance of common stock from option exercises	16						16
Issuance of common stock from option exercises, Shares				3,576
Stock-based compensation	3,453						3,453
Other comprehensive gain (loss)	30									30
Net loss	(35,340)										(35,340)
Ending balance at Jun. 30, 2020	194,704			$ 4			465,034			11	(270,345)
Ending balance, Shares at Jun. 30, 2020				45,210,653
Vesting of common stock from option exercises	5						5
Vesting of common stock from option exercises, Shares				1,011
Issuance of common stock from option exercises	9						9
Issuance of common stock from option exercises, Shares				3,706
Issuance of common stock pursuant to employee stock purchase plan	401						401
Issuance of common stock pursuant to employee stock purchase plan, Shares				44,377
Stock-based compensation	3,346						3,346
Other comprehensive gain (loss)	(11)									(11)
Net loss	(28,232)										(28,232)
Ending balance at Sep. 30, 2020	170,222			$ 4			468,795				(298,577)
Ending balance, Shares at Sep. 30, 2020				45,259,747
Beginning balance at Dec. 31, 2020	195,995			$ 5			524,358				(328,368)
Beginning balance, Shares at Dec. 31, 2020				50,265,575
Issuance of common stock, net of discounts and issuance costs			$ 1,454						$ 1,454
Issuance of common stock, net of discounts and issuance costs, Shares						114,914
Vesting of common stock from option exercises	4						4
Vesting of common stock from option exercises, Shares				1,011
Issuance of common stock from option exercises	143						143
Issuance of common stock from option exercises, Shares				55,277
Issuance of common stock pursuant to employee stock purchase plan	446						446
Issuance of common stock pursuant to employee stock purchase plan, Shares				48,792
Stock-based compensation	3,883						3,883
Other comprehensive gain (loss)	(23)									(23)
Net loss	(1,073)										1,073
Ending balance at Mar. 31, 2021	200,829			$ 5			530,288			(23)	(329,441)
Ending balance, Shares at Mar. 31, 2021				50,485,569
Beginning balance at Dec. 31, 2020	$ 195,995			$ 5			524,358				(328,368)
Beginning balance, Shares at Dec. 31, 2020				50,265,575
Issuance of common stock, net of discounts and issuance costs, Shares			114,914
Issuance of common stock from option exercises, Shares	59,465
Other comprehensive gain (loss)	$ (5)
Net loss	(62,181)
Ending balance at Sep. 30, 2021	198,571			$ 6			589,119			(5)	(390,549)
Ending balance, Shares at Sep. 30, 2021				57,149,978
Beginning balance at Mar. 31, 2021	200,829			$ 5			530,288			(23)	(329,441)
Beginning balance, Shares at Mar. 31, 2021				50,485,569
Issuance of common stock, net of discounts and issuance costs		$ 49,744			$ 1			$ 49,743
Issuance of common stock, net of discounts and issuance costs, Shares					6,596,306
Vesting of common stock from option exercises	4						4
Vesting of common stock from option exercises, Shares				1,011
Issuance of common stock from option exercises	2						2
Issuance of common stock from option exercises, Shares				4,071
Stock-based compensation	4,473						4,473
Other comprehensive gain (loss)	25									25
Net loss	(30,500)										30,500
Ending balance at Jun. 30, 2021	224,577			$ 6			584,510			2	359,941
Ending balance, Shares at Jun. 30, 2021				57,086,957
Vesting of common stock from option exercises	3						3
Vesting of common stock from option exercises, Shares				773
Issuance of common stock from option exercises, Shares				117
Issuance of common stock pursuant to employee stock purchase plan	380						380
Issuance of common stock pursuant to employee stock purchase plan, Shares				62,131
Stock-based compensation	4,226						4,226
Other comprehensive gain (loss)	(7)									(7)
Net loss	(30,608)										(30,608)
Ending balance at Sep. 30, 2021	$ 198,571			$ 6			$ 589,119			$ (5)	$ (390,549)
Ending balance, Shares at Sep. 30, 2021				57,149,978