CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - 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	(169,514)				(169,514)
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	42,354		42,354
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)		820,310
Issuance of common stock under equity incentive plans	$ 23,932		23,932
Net exercise of warrants (shares)	600,000	600,000
Net exercise of warrants	$ 0	$ 1	(1)
Unrealized gain (loss) on investments	1,395			1,395
Balance at end of period (shares) at Jun. 30, 2020		44,482,308
Balance at end of period at Jun. 30, 2020	605,004	$ 45	1,535,490	11,284	(941,815)
Balance at beginning of period (shares) at Mar. 31, 2020		43,552,312
Balance at beginning of period at Mar. 31, 2020	656,226	$ 44	1,505,431	9,707	(858,956)
Increase (Decrease) in Stockholders' Equity
Net loss	(82,859)				(82,859)
Share-based compensation expense	20,787		20,787
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)		323,789
Issuance of common stock under equity incentive plans	$ 8,749		8,749
Net exercise of warrants (shares)	600,000	600,000
Net exercise of warrants	$ 0	$ 1	(1)
Unrealized gain (loss) on investments	1,577			1,577
Balance at end of period (shares) at Jun. 30, 2020		44,482,308
Balance at end of period at Jun. 30, 2020	$ 605,004	$ 45	1,535,490	11,284	(941,815)
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	(302,110)				(302,110)
Share-based compensation expense	52,691		52,691
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)		537,032
Issuance of common stock under equity incentive plans	$ 16,494	$ 1	16,493
Net exercise of warrants (shares)	623,814	623,814
Net exercise of warrants	$ 0	$ 1	(1)
Unrealized gain (loss) on investments	$ (158)			(158)
Balance at end of period (shares) at Jun. 30, 2021	51,608,944	51,608,944
Balance at end of period at Jun. 30, 2021	$ 1,128,920	$ 52	2,551,615	9,601	(1,432,348)
Balance at beginning of period (shares) at Mar. 31, 2021		51,375,786
Balance at beginning of period at Mar. 31, 2021	1,259,413	$ 51	2,515,824	9,456	(1,265,918)
Increase (Decrease) in Stockholders' Equity
Net loss	(166,430)				(166,430)
Share-based compensation expense	27,969		27,969
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)		224,129
Issuance of common stock under equity incentive plans	6,609	$ 1	6,608
Unrealized gain (loss) on investments	$ 145			145
Balance at end of period (shares) at Jun. 30, 2021	51,608,944	51,608,944
Balance at end of period at Jun. 30, 2021	$ 1,128,920	$ 52	$ 2,551,615	$ 9,601	$ (1,432,348)