Stock Plan - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jul. 01, 2017	Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance, beginning of period (in shares)	34,454
Granted (in shares)	0
Exercised (in shares)	(3,850)
Canceled (in shares)	(2,562)
Balance, end of period (in shares)	28,042
Options exercisable (in shares)	20,405
Options vested and expected to vest (in shares)	27,831
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)
Exercised, weighted average exercise price (in dollars per share)	1.32
Canceled, weighted average exercise price (in dollars per share)	7.26
Balance, weighted average exercise price, end of period (in dollars per share)	3.88
Options exercisable, weighted average exercise price (in dollars per share)	3.08
Options vested and expected to vest, weighted average exercise price (in dollars per share)	$ 3.87
Options outstanding, aggregate intrinsic value, end of period	$ 85,564
Options exercisable, aggregate intrinsic value	72,752
Options vested and expected to vest, aggregate intrinsic value	$ 85,240
Fair value of the Class A common stock (in dollars per share)		$ 5.31