Selected Quarterly Financial Data - Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Total revenue	$ 825	$ 28,650	$ 277	$ 229	$ 565	$ 67	$ 114	$ 244	$ 29,981	$ 990	$ 2,243
Total operating expenses	4,447	9,120	6,769	6,779	10,403	9,426	8,516	7,841	27,115	36,186	35,174
Income (loss) from operations	(3,622)	19,530	(6,492)	(6,550)	(9,838)	(9,359)	(8,402)	(7,597)	2,866	(35,196)	(32,931)
Net income (loss)	$ (3,531)	$ 19,487	$ (6,491)	$ (7,574)	$ (10,329)	$ (9,693)	$ (6,906)	$ (6,524)	$ 1,891	$ (33,452)	$ (34,156)
Net income (loss) per share applicable to common stockholders—basic	$ (0.15)	$ 0.95	$ (0.33)	$ (0.39)					$ 0.09	$ (1.76)	$ (2.37)
Net income (loss) per share applicable to common stockholders-diluted	$ (0.15)	$ 0.91	$ (0.33)	$ (0.39)					$ 0.09	(1.76)	$ (2.37)
Net loss per share applicable to common stockholder Basic and Diluted					$ (0.53)	$ (0.50)	$ (0.36)	$ (0.36)		$ (1.76)
Revenues									$ 406	$ 490	$ 2,243
Transaction costs incurred in relation to business combination									2,500
Roche
Revenues		$ 29,000							$ 29,600
Viventia Bio Inc.
Transaction costs incurred in relation to business combination		$ 2,500