Employee Stock Plans - Stock Option Activity Table (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares outstanding	1,631,977	1,540,369
Shares outstanding, weighted-average exercise price	$ 63.69	$ 58.34
Shares granted	332,928
Shares granted, weighted-average exercise price	$ 81.88
Shares exercised	(176,783)
Shares exercised, weighted-average exercise price	$ 49.86
Shares forfeited	(64,537)
Shares forfeited, weighted-average exercise price	$ 67.79
Shares exercisable	787,871
Shares exercisable, weighted-average exercise price	$ 54.75
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Weighted Average Remaining Contractual Term	65 months
Shares outstanding, weighted-average remaining contractual life	81 months
Shares outstanding, aggregate intrinsic value	$ 14,401
Shares exercisable, aggregate intrinsic value	$ 11,579