Stockholders' Equity (Summary of Stock Option Activity and Weighted Average Exercise Prices) (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
Options
Beginning balance (in shares) | shares	7,769
Granted (in shares) | shares	1,553
Exercised (in shares) | shares	(777)
Cancelled or expired (in shares) | shares	(841)
Ending balance (in shares) | shares	7,704
Options vested and expected to vest (in shares) | shares	7,045
Options exercisable at end of period (in shares) | shares	5,151
Weighted Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 10.88
Granted (in dollars per share) | $ / shares	8.47
Exercised (in dollars per share) | $ / shares	8.86
Cancelled or expired (in dollars per share) | $ / shares	12.14
Ending balance (in dollars per share) | $ / shares	10.47
Options vested and expected to vest (in dollars per share) | $ / shares	10.66
Options exercisable at end of period (in dollars per share) | $ / shares	$ 11.18
Weighted Average Remaining Contractual Term (in years)
Options outstanding at end of period	6 years 1 month 21 days
Options vested and expected to vest	5 years 10 months 6 days
Options exercisable at end of period	4 years 10 months 10 days
Aggregate Intrinsic Value
Options outstanding at end of period | $	$ 26,888
Options vested and expected to vest | $	23,517
Options exercisable at end of period | $	$ 15,315