Stockholders' Equity - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance, beginning of period (in shares) | shares	16,263
Balance, end of period (in shares) | shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Balance, weighted average exercise price, beginning of period (in dollars per share) | $ / shares	$ 3.00
Balance, weighted average exercise price, end of period (in dollars per share) | $ / shares
2007 And 2015 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Granted (in shares) | shares	0
Exercised (in shares) | shares	(3,290)
Canceled (in shares) | shares	(102)
Balance, end of period (in shares) | shares	12,871
Options exercisable (in shares) | shares	12,755
Options vested and expected to vest (in shares) | shares	12,871
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Granted, weighted average exercise price (in dollars per share) | $ / shares
Exercised, weighted average exercise price (in dollars per share) | $ / shares	0.85
Canceled, weighted average exercise price (in dollars per share) | $ / shares	8.45
Balance, weighted average exercise price, end of period (in dollars per share) | $ / shares	3.51
Options exercisable, weighted average exercise price (in dollars per share) | $ / shares	3.47
Options vested and expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 3.51
Options outstanding, weighted average remaining contractual term	4 years 4 months 24 days
Options exercisable, weighted average remaining contractual term	4 years 4 months 24 days
Options vested and expected to vest, weighted average remaining contractual term	4 years 4 months 24 days
Options exercised, aggregate intrinsic value | $	$ 18,059
Options outstanding, aggregate intrinsic value | $	43,320
Options exercisable, aggregate intrinsic value | $	43,249
Options vested and expected to vest, aggregate intrinsic value | $	$ 43,320