Net Loss Per Share Computation of Basic and Diluted Net Loss Per Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator:
Net loss	$ (3,031)	$ (6,396)	$ (9,267)	$ (16,802)
Denominator:
Weighted average number of common shares outstanding (in shares)	42,648	41,617	42,428	41,384
Net loss per share, basic and diluted (in usd per share)	$ (0.07)	$ (0.15)	$ (0.22)	$ (0.41)