Condensed 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	$ 147,603	$ 57,868	$ 29,802
General and administrative	21,379	18,282	20,238
Total operating expenses	168,982	76,150	50,040
Loss from operations	(168,982)	(76,150)	(50,040)
Interest expense	(198)	(376)	(520)
Other income, net	2,192	1,548	776
Net loss	$ (166,988)	$ (74,978)	$ (49,784)
Net loss per common share (basic and diluted) (in dollars per share)	$ (6.98)	$ (3.33)	$ (2.26)
Weighted-average shares outstanding (basic and diluted)	23,933,273	22,544,475	22,019,818
Other comprehensive loss:
Unrealized (loss) gain on investments	$ (673)	$ 310	$ (423)
Total comprehensive loss	$ (167,661)	$ (74,668)	$ (50,207)