Preferred Stock and Stockholders' Equity (Summary of Stock Plan Activity) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Shares Available For Future Grant
Beginning balance (in shares)	7,726	7,630	7,920
Increase in shares authorized for grant (in shares)	4,601	4,589	4,508
Shares granted (in shares)	(4,976)	(5,599)	(5,282)
Shares canceled and forfeited (in shares)	1,273	1,106	484
Ending balance (in shares)	8,624	7,726	7,630
Shares Subject to Options Outstanding
Beginning balance (in shares)	22,826	20,454	17,663
Shares granted (in shares)	4,976	5,599	5,282
Shares exercised (in shares)	(2,929)	(2,121)	(2,007)
Shares canceled and forfeited (in shares)	(1,273)	(1,106)	(484)
Ending balance (in shares)	23,600	22,826	20,454
Options exercisable (in shares)	15,398
Options fully vested and expected to vest (in shares)	22,847
Outstanding Options, Weighted- Average Exercise Price
Beginning balance (in dollars per share)	$ 7.72	$ 5.22	$ 3.63
Shares granted (in dollars per share)	11.52	16.27	9.90
Shares exercised (in dollars per share)	3.57	4.40	3.60
Shares canceled and forfeited (in dollars per share)	12.68	11.08	5.04
Ending balance (in dollars per share)	8.77	$ 7.72	$ 5.22
Options exercisable (in dollars per share)	6.80
Options fully vested and expected to vest (in dollars per share)	$ 8.63
Outstanding Options, Weighted Average Remaining Contractual Life
Weighted average remaining contractual life	6 years 6 months
Weighted average remaining contractual life, Options exercisable	5 years 5 months 12 days
Weighted average remaining contractual life, Options fully vested and expected to vest	6 years 5 months 8 days
Outstanding Options, Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 100,062
Options exercisable	91,283
Options fully vested and expected to vest	$ 99,582