CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Revenue from collaborative arrangements	$ 1,545		$ 4,635
Operating expenses:
Research and development	11,695	$ 8,527	31,927	$ 26,338
General and administrative	5,354	4,137	14,449	12,324
Litigation expense	3,694	2,548	29,122	6,157
Total operating expenses	20,743	15,212	75,498	44,819
Loss from operations	(19,198)	(15,212)	(70,863)	(44,819)
Other income (expense):
Interest income	401	179	1,020	360
Interest expense	(223)		(399)
Total other income, net	178	179	621	360
Net loss	(19,020)	(15,033)	(70,242)	(44,459)
Dividends on redeemable convertible preferred stock		(4,111)		(6,733)
Deemed dividend related to beneficial conversion feature of redeemable convertible preferred stock				(6,144)
Net loss attributable to common stockholders	$ (19,020)	$ (19,144)	$ (70,242)	$ (57,336)
Net loss per share attributable to common stockholders – basic and diluted	$ (0.35)	$ (0.92)	$ (1.32)	$ (2.76)
Weighted average common shares outstanding – basic and diluted	54,799,644	20,841,728	53,037,516	20,809,372