Stockholders' Equity - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance, beginning of period (in shares) | shares	34,454
Granted (in shares) | shares	1,150
Exercised (in shares) | shares	(6,634)
Canceled (in shares) | shares	(6,775)
Balance, end of period (in shares) | shares	22,195
Options exercisable (in shares) | shares	16,455
Options vested and expected to vest (in shares) | shares	22,084
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)	$ 3.85
Granted, weighted average exercise price (in dollars per share)	5.63
Exercised, weighted average exercise price (in dollars per share)	1.15
Canceled, weighted average exercise price (in dollars per share)	9.59
Balance, weighted average exercise price, end of period (in dollars per share)	2.99
Options exercisable, weighted average exercise price (in dollars per share)	2.42
Options vested and expected to vest, weighted average exercise price (in dollars per share)	$ 2.99
Options outstanding, aggregate intrinsic value, end of period | $	$ 93,199
Options exercisable, aggregate intrinsic value | $	77,220
Options vested and expected to vest, aggregate intrinsic value | $	$ 92,872
Fair value of the Class A common stock (in dollars per share)	$ 6.96