Net Loss Per Share - Weighted Average Number of Common Shares Outstanding (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Numerator:
Net loss	$ (14,510)	$ (2,469)	$ (21,820)	$ (10,104)
Denominator:
Weighted average common shares outstanding	97,318,000	90,216,000	96,940,000	89,812,000
Weighted average unvested common shares subject to repurchase	(937,000)	(713,000)	(894,000)	(590,000)
Weighted average common shares outstanding-basic	96,381,000	89,503,000	96,046,000	89,222,000
Effect of dilutive securities:
Options, warrants and restricted share awards	0	0	0	0
Weighted average common shares outstanding-diluted	96,381,000	89,503,000	96,046,000	89,222,000
Net loss per common share:
Basic and diluted net loss per share	$ (0.15)	$ (0.03)	$ (0.23)	$ (0.11)