Stock-Based Compensation - Exercise Prices for Stock Options (Details) - Employee And Non Employee Stock Option [Member]	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Exercise prices for stock options outstanding and exercisable:
Number of stock options outstanding (in shares) | shares	4,951,256
Options outstanding, Weighted-average remaining contractual term	6 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 41.42
Number of stock options exercisable (in shares) | shares	3,143,656
Options exercisable, Weighted-average remaining contractual life	4 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 36.98
Range of Exercise Prices $0.00 - $20.00
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	0.00
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 20.00
Number of stock options outstanding (in shares) | shares	57,359
Options outstanding, Weighted-average remaining contractual term	3 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 18.63
Number of stock options exercisable (in shares) | shares	57,359
Options exercisable, Weighted-average remaining contractual life	3 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 18.63
Range of Exercise Prices $20.01 - $25.00
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	20.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 25.00
Number of stock options outstanding (in shares) | shares	438,614
Options outstanding, Weighted-average remaining contractual term	2 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 20.18
Number of stock options exercisable (in shares) | shares	438,614
Options exercisable, Weighted-average remaining contractual life	2 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 20.18
Range of Exercise Prices $25.01 - $30.00
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	25.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 30.00
Number of stock options outstanding (in shares) | shares	10,210
Options outstanding, Weighted-average remaining contractual term	2 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 27.95
Number of stock options exercisable (in shares) | shares	10,210
Options exercisable, Weighted-average remaining contractual life	2 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 27.95
Range of Exercise Prices $30.01 - $35.00
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	30.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 35.00
Number of stock options outstanding (in shares) | shares	352,500
Options outstanding, Weighted-average remaining contractual term	5 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 34.22
Number of stock options exercisable (in shares) | shares	352,500
Options exercisable, Weighted-average remaining contractual life	5 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 34.22
Range of Exercise Prices $35.01 - $40.00
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	35.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 40.00
Number of stock options outstanding (in shares) | shares	2,019,000
Options outstanding, Weighted-average remaining contractual term	5 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 38.20
Number of stock options exercisable (in shares) | shares	1,643,000
Options exercisable, Weighted-average remaining contractual life	4 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 38.03
Range of Exercise Prices $40.01 to $45.00
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	40.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 45.00
Number of stock options outstanding (in shares) | shares	254,000
Options outstanding, Weighted-average remaining contractual term	8 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 43.93
Number of stock options exercisable (in shares) | shares	33,200
Options exercisable, Weighted-average remaining contractual life	8 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 43.93
Range of Exercise Prices $45.01 to $50.00
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	45.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 50.00
Number of stock options outstanding (in shares) | shares	807,173
Options outstanding, Weighted-average remaining contractual term	7 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 47.57
Number of stock options exercisable (in shares) | shares	428,773
Options exercisable, Weighted-average remaining contractual life	6 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 47.68
Range of Exercise Prices $50.01 and above
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	50.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 55.00
Number of stock options outstanding (in shares) | shares	354,900
Options outstanding, Weighted-average remaining contractual term	7 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 51.98
Number of stock options exercisable (in shares) | shares	150,000
Options exercisable, Weighted-average remaining contractual life	7 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 52.05
Range Of Exercise Prices From Dollars 55.01 To 60.00 [Member]
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	55.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 60.00
Number of stock options outstanding (in shares) | shares	595,000
Options outstanding, Weighted-average remaining contractual term	9 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 56.95
Number of stock options exercisable (in shares) | shares	10,000
Options exercisable, Weighted-average remaining contractual life	4 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 56.95
Range Of Exercise Prices From Dollars 60.01 And Above [Member]
Exercise prices for stock options outstanding and exercisable:
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	$ 60.01
Number of stock options outstanding (in shares) | shares	62,500
Options outstanding, Weighted-average remaining contractual term	8 years
Options outstanding, Weighted-average exercise price (in dollars per share)	$ 60.70
Number of stock options exercisable (in shares) | shares	20,000
Options exercisable, Weighted-average remaining contractual life	5 years
Options exercisable, Weighted-average exercise price (in dollars per share)	$ 60.70