Summary of Significant Accounting Policies (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Numerator:
Net loss	$ (5,473)	$ (14,567)	$ (16,645)	$ (27,929)
Denominator:
Weighted-average common shares outstanding	33,078	17,903	32,429	17,887
Basic and diluted net loss per share	$ (0.17)	$ (0.81)	$ (0.51)	$ (1.56)