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, 2017		28,622,886
Balance at beginning of period at Dec. 31, 2017	$ 143,288	$ 29	$ 594,407	$ 9,479	$ (460,627)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(42,578)				(42,578)
Issuance of common stock, net of issuance costs (shares)		3,162,500
Issuance of common stock, net of issuance costs	130,660	$ 3	130,657
Share-based compensation expense	7,534		7,534
Issuance of common stock from ESPP (shares)		14,246
Issuance of common stock from ESPP	$ 202		202
Exercise of options for cash (shares)	513,808	513,808
Exercise of options for cash	$ 7,372		7,372
Unrealized gain (loss) on investments	(134)			(134)
Balance at end of period (shares) at Jun. 30, 2018		32,313,440
Balance at end of period at Jun. 30, 2018	246,344	$ 32	740,172	9,345	(503,205)
Balance at beginning of period (shares) at Mar. 31, 2018		29,025,834
Balance at beginning of period at Mar. 31, 2018	137,841	$ 29	603,957	9,191	(475,336)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(27,869)				(27,869)
Issuance of common stock, net of issuance costs (shares)		3,162,500
Issuance of common stock, net of issuance costs	130,660	$ 3	130,657
Share-based compensation expense	3,874		3,874
Issuance of common stock from ESPP (shares)		14,246
Issuance of common stock from ESPP	$ 202		202
Exercise of options for cash (shares)	110,860	110,860
Exercise of options for cash	$ 1,482		1,482
Unrealized gain (loss) on investments	154			154
Balance at end of period (shares) at Jun. 30, 2018		32,313,440
Balance at end of period at Jun. 30, 2018	$ 246,344	$ 32	740,172	9,345	(503,205)
Balance at beginning of period (shares) at Dec. 31, 2018	32,538,857	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
Exercise of options for cash (shares)	332,887	332,887
Exercise of options for cash	$ 4,300		4,300
Proceeds from disgorgement of stockholders' short-swing profits	$ 1,050		1,050
Net exercise of warrants (shares)	1,400,000	1,400,000
Net exercise of warrants	$ 0	$ 1	(1)
Unrealized gain (loss) on investments	$ 309			309
Balance at end of period (shares) at Jun. 30, 2019	38,551,426	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
Exercise of options for cash (shares)	97,489	97,489
Exercise of options for cash	$ 1,632		1,632
Unrealized gain (loss) on investments	$ 151			151
Balance at end of period (shares) at Jun. 30, 2019	38,551,426	38,551,426
Balance at end of period at Jun. 30, 2019	$ 472,481	$ 39	$ 1,108,306	$ 9,788	$ (645,652)