Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-In-Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Series B-2 Convertible Preferred Stock	Series B Convertible Preferred Stock	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
Balance at Dec. 31, 2013	$ (277,301)				$ (277,301)		$ 43,892	$ 78,737	$ 93,977	$ 12,232	$ 271	$ 525	$ 23,168
Balance (in shares) at Dec. 31, 2013		385,664					701,235	939,612	983,208	142,227	3,998	6,443	496,111
Increase (Decrease) in Stockholders' Equity
Net loss	(27,097)				(27,097)
Unrealized gain from available-for-sale securities	1			1
Issuance of preferred stock						26,152							10,109
Issuance of preferred stock (in shares)						448,060							186,847
Accretion of dividends on preferred stock	(9,000)		(4,542)		(4,458)	685	1,515	3,084	3,246	470
Stock-based compensation expense	1,815		1,815
Issuance of common stock, net	50,150	1	50,149
Issuance of common stock, net (in shares)		7,012,744
Conversion of convertible preferred stock into common stock	298,063	2	298,061			(26,837)	(45,407)	(81,821)	(97,223)	(12,702)	(271)	(525)	(33,277)
Conversion of convertible preferred stock, and associated accumulated dividends into common stock (in shares)		22,327,786				(448,060)	(701,235)	(939,612)	(983,208)	(142,227)	(3,998)	(6,443)	(682,958)
Reclassification of warrants liability to additional paid-in-capital	3,117		3,117
Balance at Jun. 30, 2014	$ 39,748	$ 3	$ 348,600	$ 1	$ (308,856)
Balance (in shares) at Jun. 30, 2014		29,726,194