Statements of Convertible Preferred Stock and Stockholders' Deficit (USD $) In Thousands, except Share data, unless otherwise specified	Total USD ($)	Common Stock	Additional Paid-In-Capital USD ($)	Accumulated Other Comprehensive Income (Loss) USD ($)	Accumulated Deficit USD ($)	Series B Convertible Preferred Stock USD ($)	Series A-1 Convertible Preferred Stock USD ($)	Series A-2 Convertible Preferred Stock USD ($)	Series A-3 Convertible Preferred Stock USD ($)	Series A-4 Convertible Preferred Stock USD ($)	Series A-5 Convertible Preferred Stock USD ($)	Series A-6 Convertible Preferred Stock USD ($)
Balance at Dec. 31, 2012	$ (200,661)				$ (200,661)		$ 71,957	$ 86,714	$ 11,182	$ 271	$ 525
Balance (in shares) at Dec. 31, 2012		867,204					939,612	983,208	142,227	3,998	6,443
Increase (Decrease) in Stockholders' Equity
Net loss	(27,817)				(27,817)
Unrealized gain from available-for-sale securities	3			3
Issuance of common stock	13		13
Issuance of common stock (in shares)		12,166
Issuance of preferred stock						41,514
Issuance of preferred stock (in shares)						701,235
Accretion of dividends on preferred stock	(7,950)		(798)		(7,152)	641	3,306	3,497	506
Stock-based compensation expense	785		785
Balance at Jun. 30, 2013	$ (235,627)			$ 3	$ (235,630)	$ 42,155	$ 75,263	$ 90,211	$ 11,688	$ 271	$ 525	$ 0
Balance (in shares) at Jun. 30, 2013		879,370				701,235	939,612	983,208	142,227	3,998	6,443	0