Stockholders' Equity (Summary of Stock Option Activity and Weighted Average Exercise Prices) (Details) - Jun. 30, 2015 - USD ($) $ / shares in Units, $ in Thousands	Total
Options
Options outstanding at December 31, 2014	10,769,149
Granted	738,250
Options exercised	(478,663)
Options cancelled	(926,578)
Options outstanding at June 30, 2015	10,102,158
Options vested and expected to vest at June 30, 2015	8,831,900
Options exercisable at June 30, 2015	5,025,493
Weighted Average Exercise Price
Options outstanding at December 31, 2013	$ 10.95
Options granted	10.27
Options exercised	4.31
Options cancelled	12.32
Options outstanding at June 30, 2015	11.83
Options vested and expected to vest at June 30, 2015	11.09
Options exercisable at June 30, 2015	$ 10.61
Weighted Average Remaining Contractual Term (in years)
Options outstanding at June 30, 2015	7 years 15 days
Options vested and expected to vest at June 30, 2015	6 years 8 months 45 days
Options exercisable at June 30, 2015	5 years 8 months 8 days
Aggregate Intrinsic Value
Options outstanding at June 30, 2015	$ 7,388
Options vested and expected to vest at June 30, 2015	7,302
Options exercisable at June 30, 2015	$ 6,953