CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Viventia	Common Stock	Common Stock Viventia	Additional Paid-in Capital	Additional Paid-in Capital Viventia	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2014			17,933,260
Beginning balance at Dec. 31, 2014	$ 36,826		$ 18		$ 128,558		$ (91,750)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs (in shares)			1,446,781
Issuance of common stock, 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
Issuance of common stock warrants in connection with notes payable	328				328
Stock-based compensation expense	2,529				2,529
Net (loss) income	(33,452)						(33,452)
Ending balance (in shares) at Dec. 31, 2015			19,619,124
Ending balance at Dec. 31, 2015	18,944		$ 20		144,126		(125,202)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs (in shares)			1,446,781
Exercise of stock awards and vesting of restricted stock awards (in shares)			810,538
Exercise of stock options and vesting of restricted stock awards	269		$ 1		268
Stock-based compensation expense	4,013				4,013
Issuance of common stock pursuant to the ESPP (in shares)			88,871
Issuance of common stock pursuant to the ESPP	35				35
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
Net (loss) income	1,891						1,891
Ending balance (in shares) at Dec. 31, 2016			24,531,964
Ending balance at Dec. 31, 2016	38,677		$ 25		161,963		(123,311)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASU 2016-09	0
Cumulative effect of adoption of ASU 2016-09 | ASU 2016-09					(9)		9
Issuance of common stock, net of issuance costs (in shares)			5,525,000
Issuance of common stock, net of issuance costs	$ 6,908		$ 6		6,902
Exercise of stock awards and vesting of restricted stock awards (in shares)	140,400		161,453
Exercise of stock options and vesting of restricted stock awards	$ 40				40
Stock-based compensation expense	1,381				1,381
Issuance of common stock pursuant to the ESPP (in shares)			9,148
Issuance of common stock pursuant to the ESPP	12				12
Exercise of pre-funded common stock warrants (in shares)			4,475,000
Exercise of pre-funded common stock warrants	45		$ 4		41
Net (loss) income	(29,029)						(29,029)
Ending balance (in shares) at Dec. 31, 2017			34,702,565
Ending balance at Dec. 31, 2017	$ 18,034		$ 35		$ 170,330		$ (152,331)