CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Balance at beginning of period at Dec. 31, 2019		$ 523,505	$ (66)	$ (453,527)	$ 69,912
Balance at beginning of period (in shares) at Dec. 31, 2019	41,485,638
Increase (Decrease) in Stockholders' Equity
Vesting of restricted stock units		(121)			(121)
Vesting of restricted stock units (in shares)	346,582
Fair value of warrants issued		378			378
Unrealized gain (loss) on marketable securities			60		60
Foreign currency translation adjustment			53		53
Stock-based compensation expense		3,453			3,453
Net loss				(15,586)	(15,586)
Balance at end of period at Mar. 31, 2020		527,215	47	(469,113)	58,149
Balance at end of period (in shares) at Mar. 31, 2020	41,832,220
Balance at beginning of period at Dec. 31, 2019		523,505	(66)	(453,527)	69,912
Balance at beginning of period (in shares) at Dec. 31, 2019	41,485,638
Increase (Decrease) in Stockholders' Equity
Unrealized gain (loss) on marketable securities					23
Net loss					(27,183)
Balance at end of period at Jun. 30, 2020		530,061	15	(480,710)	49,366
Balance at end of period (in shares) at Jun. 30, 2020	42,691,114
Balance at beginning of period at Dec. 31, 2019		523,505	(66)	(453,527)	69,912
Balance at beginning of period (in shares) at Dec. 31, 2019	41,485,638
Balance at end of period at Dec. 31, 2020		542,286	(94)	(504,542)	$ 37,650
Balance at end of period (in shares) at Dec. 31, 2020	45,109,314				45,109,314
Balance at beginning of period at Mar. 31, 2020		527,215	47	(469,113)	$ 58,149
Balance at beginning of period (in shares) at Mar. 31, 2020	41,832,220
Increase (Decrease) in Stockholders' Equity
Vesting of restricted stock units		(463)			(463)
Vesting of restricted stock units (in shares)	858,894
Unrealized gain (loss) on marketable securities			(37)		(37)
Foreign currency translation adjustment			5		5
Stock-based compensation expense		3,309			3,309
Net loss				(11,597)	(11,597)
Balance at end of period at Jun. 30, 2020		530,061	15	(480,710)	49,366
Balance at end of period (in shares) at Jun. 30, 2020	42,691,114
Balance at beginning of period at Dec. 31, 2020		542,286	(94)	(504,542)	$ 37,650
Balance at beginning of period (in shares) at Dec. 31, 2020	45,109,314				45,109,314
Increase (Decrease) in Stockholders' Equity
Issuance of common stock in connection with exercise of stock options and warrants and vesting of restricted stock units		(2,579)			$ (2,579)
Issuance of common stock in connection with exercise of stock options and warrants and vesting of restricted stock units (in shares)	666,144
Issuance of common stock in connection with public offering		103,348			103,348
Issuance of common stock in connection with public offering (in shares)	6,306,271
Unrealized gain (loss) on marketable securities			(35)		(35)
Foreign currency translation adjustment			(11)		(11)
Stock-based compensation expense		2,675			2,675
Net loss				(28,754)	(28,754)
Balance at end of period at Mar. 31, 2021		645,730	(140)	(533,296)	112,294
Balance at end of period (in shares) at Mar. 31, 2021	52,081,729
Balance at beginning of period at Dec. 31, 2020		542,286	(94)	(504,542)	$ 37,650
Balance at beginning of period (in shares) at Dec. 31, 2020	45,109,314				45,109,314
Increase (Decrease) in Stockholders' Equity
Unrealized gain (loss) on marketable securities					$ (10)
Net loss					(46,915)
Balance at end of period at Jun. 30, 2021	$ 1	785,455	(184)	(551,457)	$ 233,815
Balance at end of period (in shares) at Jun. 30, 2021	61,204,987				61,204,987
Balance at beginning of period at Mar. 31, 2021		645,730	(140)	(533,296)	$ 112,294
Balance at beginning of period (in shares) at Mar. 31, 2021	52,081,729
Increase (Decrease) in Stockholders' Equity
Issuance of common stock in connection with exercise of stock options and warrants and vesting of restricted stock units		1,041			1,041
Issuance of common stock in connection with exercise of stock options and warrants and vesting of restricted stock units (in shares)	1,024,666
Issuance of common stock in connection with public offering	$ 1	134,851			134,852
Issuance of common stock in connection with public offering (in shares)	8,098,592
Unrealized gain (loss) on marketable securities			25		25
Foreign currency translation adjustment			(69)		(69)
Stock-based compensation expense		3,833			3,833
Net loss				(18,161)	(18,161)
Balance at end of period at Jun. 30, 2021	$ 1	$ 785,455	$ (184)	$ (551,457)	$ 233,815
Balance at end of period (in shares) at Jun. 30, 2021	61,204,987				61,204,987