Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO [Member]	Secondary Offering [Member]	Series B Preferred Stock [Member]	Convertible preferred stock [Member]	Convertible preferred stock [Member] IPO [Member]	Convertible preferred stock [Member] Series B Preferred Stock [Member]	Convertible preferred stock [Member] Series B Preferred Stock [Member] Convertible notes [Member]	Convertible preferred stock [Member] Series C Convertible Preferred Stock [Member]	Convertible preferred stock [Member] Series D Preferred Stock [Member]	Convertible preferred stock [Member] Series D-2 Preferred [Member]	Convertible preferred stock [Member] Series E Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] IPO [Member]	Common Stock [Member] Secondary Offering [Member]	Common Stock [Member] Series B Preferred Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] IPO [Member]	Additional Paid-in Capital [Member] Secondary Offering [Member]	Additional Paid-in Capital [Member] Series B Preferred Stock [Member]	Accumulated Deficit [Member]
Beginning Balances at Dec. 31, 2012					$ 29,647
Beginning Balances at Dec. 31, 2012	$ (34,742)																$ 507				$ (35,249)
Beginning Balances, shares at Dec. 31, 2012					68,905,247
Beginning Balances, shares at Dec. 31, 2012													133,707
Conversion of convertible securities				$ 5,704			$ (5,704)	$ 4,588												$ 5,704
Conversion of convertible securities, shares							(12,674,846)	10,195,552								1,102,160
Issuance of stock									$ 19,301	$ 9,665
Issuance of stock, shares									36,444,444	17,777,777
Issuance of common stock upon exercise of options	27																27
Issuance of common stock upon exercise of options, shares													21,444
Vesting of options subject to repurchase	1																1
Stock-based compensation	215																215
Net loss	(18,497)																				(18,497)
Ending Balances at Dec. 31, 2013					$ 57,497
Ending Balances at Dec. 31, 2013	(47,292)																6,454				(53,746)
Ending Balances, shares at Dec. 31, 2013					120,648,174
Ending Balances, shares at Dec. 31, 2013													1,257,311
Conversion of convertible securities		$ 122,290				$ (122,290)								$ 2				$ 122,288
Conversion of convertible securities, shares						(182,575,322)								15,876,104
Issuance of stock		132,137																132,137
Issuance of stock, shares														6,900,000
Issuance of convertible preferred stock											$ 9,977	$ 54,816
Issuance of convertible preferred stock, shares											13,168,291	48,758,857
Reclassification of warrant liability upon closing of IPO		2,752																2,752
Reclassification of call option liability upon closing of IPO		$ 9,581																$ 9,581
Issuance of common stock upon exercise of warrants	572																572
Issuance of common stock upon exercise of warrants, shares													158,179
Issuance of common stock upon exercise of options	$ 59																59
Issuance of common stock upon exercise of options, shares	44,822												44,822
Issuance of common stock under employee benefit plans	$ 142																142
Issuance of common stock under employee benefit plans, shares													9,021
Beneficial conversion feature related to the issuance of Series E preferred stock	25,559				$ (25,559)												25,559
Deemed dividend related to beneficial conversion feature of convertible preferred stock	(25,559)				$ 25,559												(25,559)
Stock-based compensation	4,641																4,641
Net loss	(57,513)																				(57,513)
Ending Balances at Dec. 31, 2014	167,369												$ 2				278,626				(111,259)
Ending Balances, shares at Dec. 31, 2014													24,245,437
Issuance of stock			$ 80,209												$ 1				$ 80,208
Issuance of stock, shares															4,999,999
Issuance of common stock upon exercise of options	$ 121																121
Issuance of common stock upon exercise of options, shares	90,851												90,851
Issuance of common stock under employee benefit plans	$ 279																279
Issuance of common stock under employee benefit plans, shares													83,960
Stock-based compensation	10,699																10,699
Net loss	(82,177)																				(82,177)
Ending Balances at Dec. 31, 2015	$ 176,500												$ 3				$ 369,933				$ (193,436)
Ending Balances, shares at Dec. 31, 2015													29,420,247