Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $) In Thousands, except Share data	Total	IPO	Follow-on Offering	Convertible Preferred Stock	Common Stock	Common Stock IPO	Common Stock Follow-on Offering	Additional Paid-in Capital	Additional Paid-in Capital IPO	Additional Paid-in Capital Follow-on Offering	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
Balance at beginning of year at Dec. 31, 2011	$ (206,105)			$ 317,280	$ 1			$ 7,581			$ (213,686)	$ (1)
Balance at beginning of year (in shares) at Dec. 31, 2011				24,026,797	1,279,732
Exercise of employee stock options for cash (in shares)					104,417
Exercise of employee stock options for cash	317							317
Lapse of repurchase rights related to common shares issued pursuant to early exercises (in shares)					1,359
Lapse of repurchase rights related to common shares issued pursuant to early exercises	10							10
Employee stock-based compensation expense	2,665							2,665
Compensation expense relating to stock options granted to consultants	144							144
Unrealized gain (loss) on available-for-sale securities, net of tax	34											34
Net (loss) income	11,366										11,366
Balance at end of the year at Dec. 31, 2012	(191,569)			317,280	1			10,717			(202,320)	33
Balance at end of the year (in shares) at Dec. 31, 2012				24,026,797	1,385,508
Exercise of employee stock options for cash (in shares)					403,468
Exercise of employee stock options for cash	2,529							2,529
Lapse of repurchase rights related to common shares issued pursuant to early exercises (in shares)					500
Lapse of repurchase rights related to common shares issued pursuant to early exercises	4							4
Conversion of preferred stock warrants to common stock warrants	659							659
Conversion of preferred stock to common stock (in shares)				(24,026,797)	24,026,797
Conversion of preferred stock to common stock	317,280			(317,280)	24			317,256
Issuance of stock (in shares)						9,686,171	5,412,686
Issuance of stock		125,872	119,975			11	5		125,861	119,970
Employee stock-based compensation expense	4,140							4,140
Compensation expense relating to stock options granted to consultants	775							775
Unrealized gain (loss) on available-for-sale securities, net of tax	22											22
Net (loss) income	(83,352)										(83,352)
Balance at end of the year at Dec. 31, 2013	296,335				41			581,911			(285,672)	55
Balance at end of the year (in shares) at Dec. 31, 2013					40,915,130
Exercise of employee stock options for cash (in shares)	652,125				652,125
Exercise of employee stock options for cash	4,399				1			4,398
Lapse of repurchase rights related to common shares issued pursuant to early exercises (in shares)					500
Lapse of repurchase rights related to common shares issued pursuant to early exercises	4							4
Issuance of common stock upon cashless exercise of common stock warrants (shares)					40,314
Issuance of common stock upon cashless exercise of common stock warrants	0
Issuance of common stock pursuant to ESPP purchase (in shares)					28,737
Issuance of common stock pursuant to ESPP purchase	579							579
Issuance of stock (in shares)							7,130,000
Issuance of stock	174,621				7			174,614
Employee stock-based compensation expense	8,514							8,514
Compensation expense relating to stock options granted to consultants	769							769
Unrealized gain (loss) on available-for-sale securities, net of tax	(294)											(294)
Net (loss) income	(137,125)										(137,125)
Balance at end of the year at Dec. 31, 2014	$ 347,802				$ 49			$ 770,789			$ (422,797)	$ (239)
Balance at end of the year (in shares) at Dec. 31, 2014					48,766,806