CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE (LOSS) INCOME - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Total revenue	$ 0	$ 425,000	$ 29,981,000
Operating expenses:
Research and development	14,077,000	12,510,000	13,479,000
General and administrative	11,623,000	8,070,000	14,736,000
Loss (gain) from change in fair value of contingent consideration	8,800,000	9,100,000	(1,100,000)
Total operating expenses	34,500,000	29,680,000	27,115,000
(Loss) income from operations	(34,500,000)	(29,255,000)	2,866,000
Other income (expense):
Other income (expense), net	807,000	226,000	(723,000)
Interest expense	0	0	(247,000)
Total other income (expense), net	807,000	226,000	(970,000)
Net (loss) income before income taxes	(33,693,000)	(29,029,000)	1,896,000
Provision for income taxes	0	0	5,000
Net (loss) income and comprehensive (loss) income	$ (33,693,000)	$ (29,029,000)	$ 1,891,000
Net (loss) income per share applicable to common stockholders—basic (in dollars per share)	$ (0.55)	$ (1.11)	$ 0.09
Weighted-average number of common shares used in net (loss) income per share applicable to common stockholders—basic (in shares)	61,774	26,105	21,083
Net (loss) income per share applicable to common stockholders-diluted (in dollars per share)	$ (0.55)	$ (1.11)	$ 0.09
Weighted-average number of common shares used in net (loss) income per share applicable to common stockholders—diluted (in shares)	61,774	26,105	21,733
Collaboration revenue
Revenue:
Total revenue	$ 0	$ 0	$ 406,000
License revenue
Revenue:
Total revenue	$ 0	$ 425,000	$ 29,575,000