CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019		43,088,921
Beginning balance at Dec. 31, 2019	$ 221,196	$ 4	$ 636,910	$ 726	$ (416,444)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share based compensation	16,613		16,613
Issuance of common stock under the equity incentive plan and proceeds from exercise (in shares)		361,722
Issuance of common stock under the equity incentive plan and proceeds from exercise	1,345		1,345
Equity offering (in shares)		7,475,000
Equity offering, net of issuance costs	108,692	$ 1	108,691
Unrealized gain (loss) on debt securities	250			250
Foreign currency translation adjustments	(622)			(622)
ESPP stock purchase and expense (in shares)		97,544
ESPP stock purchase and expense	1,748		1,748
Net loss	(47,809)				(47,809)
Ending balance (in shares) at Sep. 30, 2020		51,023,187
Ending balance at Sep. 30, 2020	301,413	$ 5	765,307	354	(464,253)
Beginning balance (in shares) at Jun. 30, 2020		50,902,874
Beginning balance at Jun. 30, 2020	318,645	$ 5	758,945	1,399	(441,704)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share based compensation	5,139		5,139
Issuance of common stock under the equity incentive plan and proceeds from exercise (in shares)		120,313
Issuance of common stock under the equity incentive plan and proceeds from exercise	914		914
Equity offering, net of issuance costs	48		48
Unrealized gain (loss) on debt securities	(479)			(479)
Foreign currency translation adjustments	(566)			(566)
ESPP stock purchase and expense (in shares)
ESPP stock purchase and expense	261		261
Net loss	(22,549)				(22,549)
Ending balance (in shares) at Sep. 30, 2020		51,023,187
Ending balance at Sep. 30, 2020	301,413	$ 5	765,307	354	(464,253)
Beginning balance (in shares) at Dec. 31, 2020		52,248,431
Beginning balance at Dec. 31, 2020	211,213	$ 5	797,985	(902)	(585,875)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share based compensation	21,524		21,524
Issuance of common stock under the equity incentive plan and proceeds from exercise (in shares)		954,225
Issuance of common stock under the equity incentive plan and proceeds from exercise	6,679		6,679
Equity offering (in shares)		7,716,686
Equity offering, net of issuance costs	194,157	$ 1	194,156
Unrealized gain (loss) on debt securities	(714)			(714)
Foreign currency translation adjustments	1,091			1,091
ESPP stock purchase and expense (in shares)		98,887
ESPP stock purchase and expense	1,938		1,938
Net loss	(128,518)				(128,518)
Ending balance (in shares) at Sep. 30, 2021		61,018,229
Ending balance at Sep. 30, 2021	307,370	$ 6	1,022,282	(525)	(714,393)
Beginning balance (in shares) at Jun. 30, 2021		60,710,876
Beginning balance at Jun. 30, 2021	332,303	$ 6	1,011,692	(641)	(678,754)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Share based compensation	6,757		6,757
Issuance of common stock under the equity incentive plan and proceeds from exercise (in shares)		307,353
Issuance of common stock under the equity incentive plan and proceeds from exercise	3,605		3,605
Equity offering, net of issuance costs	0
Unrealized gain (loss) on debt securities	(100)			(100)
Foreign currency translation adjustments	216			216
ESPP stock purchase and expense	228		228
Net loss	(35,639)				(35,639)
Ending balance (in shares) at Sep. 30, 2021		61,018,229
Ending balance at Sep. 30, 2021	$ 307,370	$ 6	$ 1,022,282	$ (525)	$ (714,393)