CONSOLIDATED STATEMENTS OF SHAREHOLDERS' DEFICIT - USD ($) $ in Thousands	Total	JonesTrading, ATM Agreement	Common Stock	Common Stock JonesTrading, ATM Agreement	Additional Paid-in Capital	Additional Paid-in Capital JonesTrading, ATM Agreement	Accumulated Deficit
Balance (in shares) at Dec. 31, 2015			38,040,891
Balance at Dec. 31, 2015	$ (26,234)		$ 380		$ 376,528		$ (403,142)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in direct offering, net of offering costs	37,314	$ 725	$ 35	$ 1	37,279	$ 724
Issuance of common stock and pre-funded warrants, net of offering costs (shares)			3,478,260	64,565
Warrant exercises	7		$ 7		0
Issuance of common stock upon exercise of warrants (shares)			749,250
Issuance of common stock upon exercise of stock options	3,146		$ 15		3,131
Issuance of common stock upon exercise of stock options for cash (in shares)			1,486,167
Stock-based compensation	13,582				13,582
Fair value of warrants in connection with amendment to notes payable	758
Net loss	(66,745)						(66,745)
Balance (in shares) at Dec. 31, 2016			43,819,133
Balance at Dec. 31, 2016	(37,447)		$ 438		432,002		(469,887)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in direct offering, net of offering costs	63,657		$ 30		63,627
Issuance of common stock and pre-funded warrants, net of offering costs (shares)			3,000,000
Issuance of common stock upon exercise of stock options	11,769		$ 14		11,755
Issuance of common stock upon exercise of stock options for cash (in shares)			1,392,093
Stock-based compensation	12,688				12,688
Net loss	(53,481)						(53,481)
Balance (in shares) at Dec. 31, 2017			48,211,226
Balance at Dec. 31, 2017	(2,814)		$ 482		520,072		(523,368)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Warrant exercises	1,424				1,424
Issuance of common stock upon exercise of stock options	$ 6,732		$ 8		6,724
Issuance of common stock upon exercise of stock options for cash (in shares)	765,949		800,458
Stock-based compensation	$ 11,713				11,713
Premium paid for Capped Call in connection with Convertible Notes	(33,180)				(33,180)
Fair value of warrants in connection with amendment to notes payable	55,655				55,655
Tax benefit related to equity component of Convertible Notes	(12,929)				(12,929)
Net loss	(126,757)						(126,757)
Balance (in shares) at Dec. 31, 2018			49,011,684
Balance at Dec. 31, 2018	$ (100,156)		$ 490		$ 549,479		$ (650,125)