Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Viventia	Initial Public Offering (IPO)	Preferred Stock Series A Convertible Preferred Stock	Preferred Stock Series B Convertible Preferred Stock	Common Stock	Common Stock Viventia	Common Stock Initial Public Offering (IPO)	Additional Paid-in Capital	Additional Paid-in Capital Viventia	Additional Paid-in Capital Initial Public Offering (IPO)	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2013				45,250,000	7,203,845	1,636,137
Beginning balance at Dec. 31, 2013	$ (54,332)			$ 45,035	$ 11,643	$ 2			$ 3,260			$ (57,594)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance due to initial public offering (in shares)				(45,250,000)	(7,203,845)
Initial public offering, net of issuance costs of $7.3 million				$ (45,035)	$ (11,643)
Issuance of common stock (in shares)						1,743,680		14,010,424
Issuance of common stock and initial public offering, net of issuance costs	15,419		$ 106,882			$ 2		$ 14	15,417		$ 106,868
Exercise of stock awards and vesting of restricted stock awards (in shares)						190,701
Exercise of stock options and vesting of restricted stock awards	65								65
Exercise of stock warrants (in shares)						352,318
Exercise of stock warrants	15								15
Conversion of preferred stock warrant to common stock warrant	247								247
Issuance of common stock warrants in connection with notes payable	254								254
Stock-based compensation expense	2,432								2,432
Ending balance at Dec. 31, 2014	36,826			$ 0	$ 0	$ 18			128,558			(91,750)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(34,156)											(34,156)
Ending balance (in shares) at Dec. 31, 2014				0	0	17,933,260
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)						1,446,781
Issuance of common stock and initial public offering, net of issuance costs	12,650					$ 2			12,648
Exercise of stock awards and vesting of restricted stock awards (in shares)						239,083
Exercise of stock options and vesting of restricted stock awards	63								63
Conversion of preferred stock warrant to common stock warrant	0
Issuance of common stock warrants in connection with notes payable	328								328
Stock-based compensation expense	2,529								2,529
Ending balance at Dec. 31, 2015	18,944			$ 0	$ 0	$ 20			144,126			(125,202)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ (33,452)											(33,452)
Ending balance (in shares) at Dec. 31, 2015				0	0	19,619,124
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in connection with the acquisition of Viventia (in shares)							4,013,431
Issuance of common stock in connection with the acquisition of Viventia		$ 13,525					$ 4			$ 13,521
Exercise of stock awards and vesting of restricted stock awards (in shares)	656,532					810,538
Exercise of stock options and vesting of restricted stock awards	$ 269					$ 1			268
Issuance of common stock pursuant to the ESPP (in shares)						88,871
Issuance of common stock pursuant to the ESPP	35								35
Conversion of preferred stock warrant to common stock warrant	0
Stock-based compensation expense	4,013								4,013
Ending balance at Dec. 31, 2016	38,677			$ 0	$ 0	$ 25			$ 161,963			(123,311)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 1,891											$ 1,891
Ending balance (in shares) at Dec. 31, 2016				0	0	24,531,964