Consolidated statements of operations and comprehensive loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating expenses
Research and development	$ 36,267	$ 28,382	$ 15,799
General and administrative	14,852	9,263	5,541
Total operating expenses	51,119	37,645	21,340
Other income (expenses)
Interest expense	(4)	(1)
Other income (expenses) (Note 8)	940	644	(520)
Total Other income (expenses)	936	643	(520)
Net loss	$ (50,183)	$ (37,002)	$ (21,860)
Net loss per common stock - basic and diluted (Note 9)	$ (2.14)	$ (1.96)	$ (1.73)
Basic and diluted weighted average number of common stock outstanding (Note 9)	23,450,315	18,893,515	12,637,839
Comprehensive loss:
Net loss	$ (50,183)	$ (37,002)	$ (21,860)
Other comprehensive income (loss) - unrealized gain (loss) on available-for-sale securities	99	121	(286)
Comprehensive loss	$ (50,084)	$ (36,881)	$ (22,146)