Statements of Convertible Preferred Stock and Stockholders' Deficit - USD ($) $ in Thousands	Series B-2 Convertible Preferred Stock	Series B	Series A-1 Convertible Preferred Stock	Series A-2 Convertible Preferred Stock	Series A-3 Convertible Preferred Stock	Series A-4 Convertible Preferred Stock	Series A-5 Convertible Preferred Stock	Series A-6 Convertible Preferred Stock	Common Stock	Additional Paid-In-Capital		Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit		Total
Balance at Dec. 31, 2012			$ 71,957	$ 86,714	$ 11,182	$ 271	$ 525						$ (200,661)		$ (200,661)
Balance (in shares) at Dec. 31, 2012			939,612	983,208	142,227	3,998	6,443		380,328
Increase (Decrease) in Stockholders' Equity
Net loss													(60,690)		(60,690)
Stock options exercised										$ 13					13
Stock options exercised (in shares)									5,336
Issuance of preferred stock		$ 41,514						$ 23,168
Issuance of preferred stock (in shares)		701,235						496,111
Accretion of dividends on preferred stock		$ (2,378)	$ (6,780)	$ (7,263)	$ (1,050)					(1,521)	[1]		(15,950)	[1]	(17,471)	[1]
Stock-based compensation expense										1,508					1,508
Balance at Dec. 31, 2013		$ 43,892	$ 78,737	$ 93,977	$ 12,232	$ 271	$ 525	$ 23,168					(277,301)		(277,301)
Balance (in shares) at Dec. 31, 2013		701,235	939,612	983,208	142,227	3,998	6,443	496,111	385,664
Increase (Decrease) in Stockholders' Equity
Net loss													(62,479)		(62,479)
Unrealized gain (loss) from marketable securities												$ (21)			(21)
Stock options exercised										170					170
Stock options exercised (in shares)									49,382
Issuance of preferred stock	$ 26,152							$ 10,109
Issuance of preferred stock (in shares)	448,060							186,847
Accretion of dividends on preferred stock	$ (685)	$ (1,515)	$ (3,084)	$ (3,246)	$ (470)					(4,542)			(4,458)		(9,000)
Issuance of warrants										41					41
Exercise of warrants (in shares)									20,435
Stock-based compensation expense										7,070					7,070
Issuance of common stock, net									$ 1	103,803					103,804
Issuance of common stock (in shares)									10,141,268
Conversion of convertible preferred stock into common stock	$ (26,837)	$ (45,407)	$ (81,821)	$ (97,223)	$ (12,702)	$ (271)	$ (525)	$ (33,277)	$ 2	298,061					298,063
Conversion of convertible preferred stock into common stock (in shares)	(448,060)	(701,235)	(939,612)	(983,208)	(142,227)	(3,998)	(6,443)	(682,958)	22,327,786
Reclassification of warrant liability to additional paid-in-capital										3,117					3,117
Balance at Dec. 31, 2014									$ 3	407,720		(21)	(344,238)		63,464
Balance (in shares) at Dec. 31, 2014									32,924,535
Increase (Decrease) in Stockholders' Equity
Net loss													(101,526)		(101,526)
Unrealized gain (loss) from marketable securities												26			26
Stock options exercised										2,337					2,337
Stock options exercised (in shares)									267,684
Exercise of warrants (in shares)									529,862
Stock-based compensation expense										14,734					14,734
Issuance of common stock, net									$ 1	482,249					482,250
Issuance of common stock (in shares)									9,262,162
Balance at Dec. 31, 2015									$ 4	$ 907,040		$ 5	$ (445,764)		$ 461,285
Balance (in shares) at Dec. 31, 2015									42,984,243

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