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, 2018		32,538,857
Balance at beginning of period at Dec. 31, 2018	$ 201,576	$ 33	$ 751,109	$ 9,479	$ (559,045)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(86,607)				(86,607)
Issuance of common stock, net of issuance costs (shares)		4,269,838
Issuance of common stock, net of issuance costs	327,810	$ 5	327,805
Share-based compensation expense	23,720		23,720
Issuance of common stock from ESPP (shares)		9,844
Issuance of common stock from ESPP	323		323
Issuance of common stock under equity incentive plans (shares)		332,887
Issuance of common stock under equity incentive plans	$ 4,300		4,300
Net exercise of warrants (shares)	1,400,000	1,400,000
Net exercise of warrants		$ 1	(1)
Proceeds from disgorgement of shareholders' short-swing profits	$ 1,050		1,050
Unrealized gain (loss) on investments	309			309
Balance at end of period (shares) at Jun. 30, 2019		38,551,426
Balance at end of period at Jun. 30, 2019	472,481	$ 39	1,108,306	9,788	(645,652)
Balance at beginning of period (shares) at Mar. 31, 2019		36,029,093
Balance at beginning of period at Mar. 31, 2019	283,554	$ 36	873,838	9,637	(599,957)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(45,695)				(45,695)
Issuance of common stock, net of issuance costs (shares)		2,415,000
Issuance of common stock, net of issuance costs	219,927	$ 3	219,924
Share-based compensation expense	12,589		12,589
Issuance of common stock from ESPP (shares)		9,844
Issuance of common stock from ESPP	323		323
Issuance of common stock under equity incentive plans (shares)		97,489
Issuance of common stock under equity incentive plans	1,632		1,632
Unrealized gain (loss) on investments	151			151
Balance at end of period (shares) at Jun. 30, 2019		38,551,426
Balance at end of period at Jun. 30, 2019	$ 472,481	$ 39	1,108,306	9,788	(645,652)
Balance at beginning of period (shares) at Dec. 31, 2019	39,517,329	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 for the period	(169,514)				(169,514)
Issuance of common stock, net of issuance costs (shares)		3,538,462
Issuance of common stock, net of issuance costs	323,977	$ 4	323,973
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		$ 1	(1)
Proceeds from disgorgement of shareholders' short-swing profits	$ 41		41
Unrealized gain (loss) on investments	$ 1,395			1,395
Balance at end of period (shares) at Jun. 30, 2020	44,482,308	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 for the period	(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		$ 1	(1)
Unrealized gain (loss) on investments	$ 1,577			1,577
Balance at end of period (shares) at Jun. 30, 2020	44,482,308	44,482,308
Balance at end of period at Jun. 30, 2020	$ 605,004	$ 45	$ 1,535,490	$ 11,284	$ (941,815)