Stock Plans (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Summary of Stock Option and RSA Activity
Beginning Balance, Shares | shares	10,272
Stock Options Granted, shares | shares	869
Stock Options Exercised, shares | shares	(3,766)
Forfeited, shares | shares	(102)
Stock Options Expired, shares | shares	(11)
Ending Balance, Shares | shares	7,262
Beginning balance, weighted average exercise price | $ / shares	$ 47.68
Stock Options Granted, weighted average exercise price | $ / shares	87.19
Stock Options Exercised, weighted average exercise price | $ / shares	34.48
Stock Options Forfeitures, weighted average exercise price | $ / shares	67.57
Stock Options Expired, weighted average exercise price | $ / shares	86.11
Ending balance, weighted average exercise price | $ / shares	$ 58.92
Options vested and expected to vest, shares | shares	7,194
Options vested and expected to vest, Weighted Average Exercise Price | $ / shares	$ 58.86
Options exercisable, shares | shares	3,399
Options exercisable, Weighted Average Exercise Price | $ / shares	$ 45.93
Beginning balance, shares | shares	7,500
RSAs Granted, shares | shares	2,670
Vested, shares | shares	(2,335)
Forfeited, shares | shares	(620)
Ending balance, shares | shares	7,215
Beginning Balance, Weighted Average Grant Price | $ / shares	$ 69.22
Granted, Weighted Average Grant Price | $ / shares	77.8
RSAs Vested, Weighted Average Grant Price | $ / shares	75.85
RSAs Forfeited, Weighted Average Grant Price | $ / shares	68.8
Ending Balance, Weighted Average Grant Price | $ / shares	$ 70.29