Net Loss Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Net loss	$ (19,512)	$ (17,961)	$ (27,817)	$ (30,833)
Accretion of Preferred Stock	(4,368)	(3,456)	(7,950)	(6,810)
Loss attributable to common stockholders - basic and diluted	$ (23,880)	$ (21,417)	$ (35,767)	$ (37,643)
Denominator:
Weighted-average number of common shares used in (loss) earnings per share - basic and diluted	869,878	854,517	868,548	815,053
(Loss) earnings per share - basic and diluted (in dollars per share)	$ (27.45)	$ (25.06)	$ (41.18)	$ (46.18)