CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional paid-in capital	Accumulated other comprehensive income	Accumulated deficit
Balance at beginning of period (shares) at Dec. 31, 2019		39,517,329
Balance at beginning of period at Dec. 31, 2019	$ 382,295	$ 40	$ 1,144,667	$ 9,889	$ (772,301)
Increase (Decrease) in Stockholders' Equity
Net loss	(256,850)				(256,850)
Issuance of common stock, net of issuance costs (shares)		3,538,462
Issuance of common stock, net of issuance costs	324,018	$ 4	324,014
Share-based compensation expense	64,104		64,104
Issuance of common stock from ESPP (shares)		6,207
Issuance of common stock from ESPP	524		524
Issuance of common stock under equity incentive plans (shares)		1,092,468
Issuance of common stock under equity incentive plans	$ 36,284	$ 1	36,283
Net exercise of warrants (shares)	600,000	600,000
Unrealized gain (loss) on investments	$ 568			568
Balance at end of period (shares) at Sep. 30, 2020		44,754,466
Balance at end of period at Sep. 30, 2020	550,943	$ 45	1,569,592	10,457	(1,029,151)
Balance at beginning of period (shares) at Jun. 30, 2020		44,482,308
Balance at beginning of period at Jun. 30, 2020	605,004	$ 45	1,535,490	11,284	(941,815)
Increase (Decrease) in Stockholders' Equity
Net loss	(87,336)				(87,336)
Share-based compensation expense	21,751		21,751
Issuance of common stock under equity incentive plans (shares)		272,158
Issuance of common stock under equity incentive plans	12,351		12,351
Unrealized gain (loss) on investments	(827)			(827)
Balance at end of period (shares) at Sep. 30, 2020		44,754,466
Balance at end of period at Sep. 30, 2020	$ 550,943	$ 45	1,569,592	10,457	(1,029,151)
Balance at beginning of period (shares) at Dec. 31, 2020	50,439,069	50,439,069
Balance at beginning of period at Dec. 31, 2020	$ 1,360,789	$ 50	2,481,218	9,759	(1,130,238)
Increase (Decrease) in Stockholders' Equity
Net loss	(382,164)				(382,164)
Share-based compensation expense	79,624		79,624
Issuance of common stock from ESPP (shares)		9,029
Issuance of common stock from ESPP	1,214		1,214
Issuance of common stock under equity incentive plans (shares)		695,171
Issuance of common stock under equity incentive plans	$ 24,726	$ 1	24,725
Net exercise of warrants (shares)	623,814	623,814
Net exercise of warrants	$ 0	$ 1	(1)
Unrealized gain (loss) on investments	$ (164)			(164)
Balance at end of period (shares) at Sep. 30, 2021	51,767,083	51,767,083
Balance at end of period at Sep. 30, 2021	$ 1,084,025	$ 52	2,586,780	9,595	(1,512,402)
Balance at beginning of period (shares) at Jun. 30, 2021		51,608,944
Balance at beginning of period at Jun. 30, 2021	1,128,920	$ 52	2,551,615	9,601	(1,432,348)
Increase (Decrease) in Stockholders' Equity
Net loss	(80,054)				(80,054)
Share-based compensation expense	26,933		26,933
Issuance of common stock under equity incentive plans (shares)		158,139
Issuance of common stock under equity incentive plans	8,232		8,232
Unrealized gain (loss) on investments	$ (6)			(6)
Balance at end of period (shares) at Sep. 30, 2021	51,767,083	51,767,083
Balance at end of period at Sep. 30, 2021	$ 1,084,025	$ 52	$ 2,586,780	$ 9,595	$ (1,512,402)