Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $)	Total USD ($)	IPO [Member] USD ($)	Series A Preferred Stock [Member] USD ($)	Series B Preferred Stock [Member] USD ($)	Series B Preferred Stock [Member] Issuance Date of January and May 2012 [Member] USD ($)	Series E Preferred Stock [Member] USD ($)	Series C Convertible Preferred Stock [Member] USD ($)	Convertible preferred stock [Member] USD ($)	Convertible preferred stock [Member] IPO [Member] USD ($)	Convertible preferred stock [Member] Series A Preferred Stock [Member] USD ($)	Convertible preferred stock [Member] Series A Preferred Stock [Member] Issuance Date of December 2008 [Member] USD ($)	Convertible preferred stock [Member] Series A Preferred Stock [Member] Issuance Date of May and December 2009 and April 2010 [Member] USD ($)	Convertible preferred stock [Member] Series B Preferred Stock [Member] USD ($)	Convertible preferred stock [Member] Series B Preferred Stock [Member] Issuance Date of February 2011 [Member] USD ($)	Convertible preferred stock [Member] Series B Preferred Stock [Member] Issuance Date of January 2012 [Member] USD ($)	Convertible preferred stock [Member] Series B Preferred Stock [Member] Issuance Date of May 2012 [Member] USD ($)	Convertible preferred stock [Member] Series B Preferred Stock [Member] Issuance Date of January and May 2012 [Member] USD ($)	Convertible preferred stock [Member] Series B Preferred Stock [Member] Convertible notes [Member] USD ($)	Convertible preferred stock [Member] Series B Preferred Stock [Member] Convertible notes [Member] Issuance Date of February 2011 [Member] USD ($)	Convertible preferred stock [Member] Series E Preferred Stock [Member] USD ($)	Convertible preferred stock [Member] Series C Convertible Preferred Stock [Member] USD ($)	Convertible preferred stock [Member] Series D Preferred Stock [Member] USD ($)	Convertible preferred stock [Member] Series D-2 Preferred [Member] USD ($)	Common Stock [Member] USD ($)	Common Stock [Member] IPO [Member] USD ($)	Common Stock [Member] Series B Preferred Stock [Member]	Additional Paid-in Capital [Member] USD ($)	Additional Paid-in Capital [Member] IPO [Member] USD ($)	Additional Paid-in Capital [Member] Series B Preferred Stock [Member] USD ($)	Additional Paid-in Capital [Member] Series B Preferred Stock [Member] Issuance Date of January and May 2012 [Member] USD ($)	Additional Paid-in Capital [Member] Series E Preferred Stock [Member] USD ($)	Deficit Accumulated During the Development Stage [Member] USD ($)	Deficit Accumulated During the Development Stage [Member] Series A Preferred Stock [Member] USD ($)
Beginning Balances at Dec. 10, 2008
Issuance of Series A convertible preferred stock valued at $0.0001 per share in consideration for research and development license in December 2008											$ 1,000
Issuance of Series A convertible preferred stock valued at $0.0001 per share in consideration for research and development license in December 2008, shares											11,000,000
Accretion to redemption value of convertible preferred stock	(10,999,000)							10,999,000																								(10,999,000)
Issuance of Series A convertible preferred stock for cash at $1.00 per share, net of issuance costs of $3, in May and December 2009 and April 2010												10,997,000
Issuance of Series A convertible preferred stock for cash at $1.00 per share, net of issuance costs of $3, in May and December 2009 and April 2010, shares												11,000,000
Accretion to redemption value of convertible preferred stock- offering costs	(3,000)							3,000																								(3,000)
Issuance of common stock upon exercise of options subject to repurchase, shares																								127,536
Extinguishment of Series A convertible preferred stock (Refer to Note 8)			12,100,000							(12,100,000)																							12,100,000
Issuance of stock														8,215,000
Issuance of stock, shares														21,805,693
Conversion of convertible securities																			4,607,000
Conversion of convertible securities, shares																			10,238,444
Issuance of common stock upon exercise of options	3,000																										3,000
Issuance of common stock upon exercise of options, shares																								2,261
Vesting of options subject to repurchase	11,000																										11,000
Stock-based compensation	192,000																										192,000
Net loss	(23,130,000)																															(23,130,000)
Ending Balances at Dec. 31, 2011	(21,826,000)																										206,000					(22,032,000)
Ending Balances at Dec. 31, 2011								22,722,000
Ending Balances, shares at Dec. 31, 2011																								129,797
Ending Balances, shares at Dec. 31, 2011								54,044,137
Issuance of stock					152,000										2,999,000	3,026,000	900,000													152,000
Issuance of stock, shares															6,430,555	6,430,555	2,000,000
Issuance of common stock upon exercise of options	5,000																										5,000
Issuance of common stock upon exercise of options, shares																								3,910
Vesting of options subject to repurchase	3,000																										3,000
Stock-based compensation	141,000																										141,000
Net loss	(13,217,000)																															(13,217,000)
Ending Balances at Dec. 31, 2012	(34,742,000)																										507,000					(35,249,000)
Ending Balances at Dec. 31, 2012								29,647,000
Ending Balances, shares at Dec. 31, 2012																								133,707
Ending Balances, shares at Dec. 31, 2012								68,905,247
Issuance of stock, shares																					14,222,222
Ending Balances at Jan. 31, 2013
Beginning Balances at Dec. 31, 2012	(34,742,000)																										507,000					(35,249,000)
Beginning Balances at Dec. 31, 2012								29,647,000
Beginning Balances, shares at Dec. 31, 2012																								133,707
Beginning Balances, shares at Dec. 31, 2012								68,905,247
Issuance of stock																					19,301,000	9,665,000
Issuance of stock, shares																					36,444,444	17,777,777
Conversion of convertible securities				5,704,000									(5,704,000)					4,588,000											5,704,000
Conversion of convertible securities, shares													(12,674,846)					10,195,552								1,102,160
Issuance of common stock upon exercise of options	27,000																										27,000
Issuance of common stock upon exercise of options, shares	21,444																							21,444
Vesting of options subject to repurchase	1,000																										1,000
Stock-based compensation	215,000																										215,000
Net loss	(18,497,000)																															(18,497,000)
Ending Balances at Dec. 31, 2013	(47,292,000)																										6,454,000					(53,746,000)
Ending Balances at Dec. 31, 2013	57,497,000		9,900,000	18,631,000			19,301,000	57,497,000
Ending Balances, shares at Dec. 31, 2013																								1,257,311
Ending Balances, shares at Dec. 31, 2013	120,648,174		22,000,000	44,425,953			36,444,444	120,648,174
Issuance of stock		132,137,000																										132,137,000
Issuance of stock, shares																									6,900,000
Conversion of convertible securities		122,290,000							(122,290,000)																2,000			122,288,000
Conversion of convertible securities, shares									(182,575,322)																15,876,104
Issuance of convertible preferred stock																				54,816,000			9,977,000
Issuance of convertible preferred stock, shares																				48,758,857			13,168,291
Reclassification of warrant liability upon closing of IPO		2,752,000																										2,752,000
Reclassification of call option liability upon closing of IPO		9,581,000																										9,581,000
Issuance of common stock upon exercise of warrants	572,000																										572,000
Issuance of common stock upon exercise of warrants, shares																								158,179
Issuance of common stock upon exercise of options	59,000																										59,000
Issuance of common stock upon exercise of options, shares	44,822																							44,822
Issuance of common stock under employee benefit plans	142,000																										142,000
Issuance of common stock under employee benefit plans, shares																								9,021
Beneficial conversion feature related to the issuance of Series E preferred stock						25,559,000														(25,559,000)											25,559,000
Deemed dividend related to beneficial conversion feature of convertible preferred stock	(25,559,000)					(25,559,000)														25,559,000											(25,559,000)
Stock-based compensation	4,641,000																										4,641,000
Net loss	(57,513,000)																															(57,513,000)
Ending Balances at Dec. 31, 2014	$ 167,369,000																							$ 2,000			$ 278,626,000					$ (111,259,000)
Ending Balances, shares at Dec. 31, 2014																								24,245,437
Ending Balances, shares at Dec. 31, 2014	0