Stockholders' Equity (Summary of Stock Option Activity and Weighted Average Exercise Prices) (Details) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Options
Beginning balance (in shares) | shares	6,266
Granted (in shares) | shares	241
Exercised (in shares) | shares	(626)
Cancelled or expired (in shares) | shares	(124)
Ending balance (in shares) | shares	5,757
Options vested and expected to vest (in shares) | shares	5,157
Options exercisable at end of period (in shares) | shares	3,093
Weighted Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 12.13
Granted (in dollars per share) | $ / shares	23.75
Exercised (in dollars per share) | $ / shares	10.36
Cancelled or expired (in dollars per share) | $ / shares	11.96
Ending balance (in dollars per share) | $ / shares	12.81
Options vested and expected to vest (in dollars per share) | $ / shares	12.50
Options exercisable at end of period (in dollars per share) | $ / shares	$ 11.38
Weighted Average Remaining Contractual Term (in years)
Options outstanding at end of period	6 years 8 months 23 days
Options vested and expected to vest	6 years 5 months 23 days
Options exercisable at end of period	4 years 11 months 19 days
Aggregate Intrinsic Value
Options outstanding at end of period | $	$ 93,297
Options vested and expected to vest | $	85,169
Options exercisable at end of period | $	$ 54,556