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	(14,709)				(14,709)
Share-based compensation expense	3,660		3,660
Exercise of options for cash (shares)		402,948
Exercise of options for cash	5,890		5,890
Unrealized gain (loss) on investments	(288)			(288)
Balance at end of period (shares) at Mar. 31, 2018		29,025,834
Balance at end of period at Mar. 31, 2018	137,841	$ 29	603,957	9,191	(475,336)
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	$ (70,146)
Exercise of options for cash (shares)	716,409
Unrealized gain (loss) on investments	$ (35)
Balance at end of period (shares) at Sep. 30, 2018		32,516,041
Balance at end of period at Sep. 30, 2018	225,089	$ 33	746,385	9,444	(530,773)
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
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)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(27,568)				(27,568)
Share-based compensation expense	$ 4,058		4,058
Exercise of options for cash (shares)	202,601	202,601
Exercise of options for cash	$ 2,156	$ 1	2,155
Unrealized gain (loss) on investments	99			99
Balance at end of period (shares) at Sep. 30, 2018		32,516,041
Balance at end of period at Sep. 30, 2018	$ 225,089	$ 33	746,385	9,444	(530,773)
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	(40,912)				(40,912)
Issuance of common stock, net of issuance costs (shares)		1,854,838
Issuance of common stock, net of issuance costs	107,883	$ 2	107,881
Share-based compensation expense	11,131		11,131
Exercise of options for cash (shares)		235,398
Exercise of options for cash	2,668		2,668
Proceeds from disgorgement of stockholders' short-swing profits	1,050		1,050
Net exercise of warrants (shares)		1,400,000
Net exercise of warrants	0	$ 1	(1)
Unrealized gain (loss) on investments	158			158
Balance at end of period (shares) at Mar. 31, 2019		36,029,093
Balance at end of period at Mar. 31, 2019	$ 283,554	$ 36	873,838	9,637	(599,957)
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	$ (140,880)
Exercise of options for cash (shares)	424,144
Net exercise of warrants (shares)	2,125,000
Unrealized gain (loss) on investments	$ 412
Balance at end of period (shares) at Sep. 30, 2019	39,367,683	39,367,683
Balance at end of period at Sep. 30, 2019	$ 434,489	$ 39	1,124,484	9,891	(699,925)
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
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
Balance at end of period at Jun. 30, 2019	472,481	$ 39	1,108,306	9,788	(645,652)
Increase (Decrease) in Stockholders' Equity
Net loss for the period	(54,273)				(54,273)
Share-based compensation expense	$ 15,106		15,106
Exercise of options for cash (shares)	91,257	91,257
Exercise of options for cash	$ 1,072		1,072
Net exercise of warrants (shares)	725,000	725,000
Net exercise of warrants	$ 0
Unrealized gain (loss) on investments	$ 103			103
Balance at end of period (shares) at Sep. 30, 2019	39,367,683	39,367,683
Balance at end of period at Sep. 30, 2019	$ 434,489	$ 39	$ 1,124,484	$ 9,891	$ (699,925)