Condensed Consolidated Statement of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $)	Total	Common stock [Member]	Additional paid-in capital [Member]	Accumulated deficit [Member]	Convertible preferred stock [Member]	Convertible preferred stock [Member] Series A [Member]	Convertible preferred stock [Member] Series B [Member]	Convertible preferred stock [Member] Series C [Member]
Beginning balance at Dec. 31, 2012	$ (74,247,000)		$ 1,322,000	$ (75,569,000)	$ 39,612,000	$ 3,747,000	$ 10,758,000	$ 25,107,000
Beginning balance, shares at Dec. 31, 2012		1,267,000			8,504,000	1,484,000	2,242,000	4,778,000
Net loss	(18,498,000)			(18,498,000)
Exercise of stock options, shares	93,000	93,000
Exercise of stock options	81,000		81,000
Share-based compensation	1,125,000		1,125,000
Deemed dividend, convertible notes	(1,378,000)			(1,378,000)
Cash exercise of preferred stock warrants, shares					10,000		10,000
Cash exercise of preferred stock warrants					47,000		47,000
Net exercise of preferred stock warrants, shares		71,000
Net exercise of preferred stock warrants
Conversion of preferred stock into common stock, shares		8,514,000			(8,514,000)	(1,484,000)	(2,252,000)	(4,778,000)
Conversion of preferred stock into common stock	39,659,000		39,659,000		(39,659,000)	(3,747,000)	(10,805,000)	(25,107,000)
Convertible notes converted into common stock, shares		3,741,000
Convertible notes converted into common stock	44,890,000		44,890,000
Cash exercise of common stock warrants, shares		3,000
Cash exercise of common stock warrants	25,000		25,000
Net exercise of common stock warrants, shares		47,000
Net exercise of common stock warrants
Reclassification of warrants from liability to equity	2,669,000		2,669,000
Issuance of common stock upon initial public offering, net of offering costs and underwriter commission, shares		5,463,000
Issuance of common stock upon initial public offering, net of offering costs and underwriter commission	56,105,000		56,105,000
Ending balance at Sep. 30, 2013	$ 50,431,000		$ 145,876,000	$ (95,445,000)
Ending balance, shares at Sep. 30, 2013		19,199,000			0	0	0	0