Stockholders' Equity (Summary of Stock Option Activity and Weighted Average Exercise Prices) (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Options
Options outstanding at December 31, 2014 | shares	10,769,149
Granted | shares	792,250
Options exercised | shares	(576,577)
Options cancelled | shares	(1,415,553)
Options outstanding at June 30, 2015 | shares	9,569,269
Options vested and expected to vest at June 30, 2015 | shares	8,582,041
Options exercisable at June 30, 2015 | shares	5,448,479
Weighted Average Exercise Price
Options outstanding at December 31, 2013	$ 10.95
Options granted	10.22
Options exercised	4.37
Options cancelled	12.20
Options outstanding at June 30, 2015	11.09
Options vested and expected to vest at June 30, 2015	11.11
Options exercisable at June 30, 2015	$ 10.91
Weighted Average Remaining Contractual Term (in years)
Options outstanding at June 30, 2015	6 years 9 months 29 days
Options vested and expected to vest at June 30, 2015	6 years 7 months 10 days
Options exercisable at June 30, 2015	5 years 7 months 21 days
Aggregate Intrinsic Value
Options outstanding at June 30, 2015 | $	$ 3,155
Options vested and expected to vest at June 30, 2015 | $	3,155
Options exercisable at June 30, 2015 | $	$ 3,155