Stock-based Compensation Expense and Share Repurchase - Stock Options Outstanding and Exercisable (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price range, options outstanding (in shares) | shares	9,955
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	7 years 3 months 18 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 103.03
Exercise price range, options exercisable (in shares) | shares	4,738
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 84.36
$26.73–$40.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	26.73
Exercise price, high end of range (in dollars per share)	$ 40
Exercise price range, options outstanding (in shares) | shares	726
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	1 year 7 months 17 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 34.46
Exercise price range, options exercisable (in shares) | shares	726
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 34.46
$40.01–$60.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	40.01
Exercise price, high end of range (in dollars per share)	$ 60
Exercise price range, options outstanding (in shares) | shares	588
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	4 years 2 months 27 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 49.43
Exercise price range, options exercisable (in shares) | shares	588
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 49.43
$60.01–$80.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	60.01
Exercise price, high end of range (in dollars per share)	$ 80
Exercise price range, options outstanding (in shares) | shares	644
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	5 years 11 months 16 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 75.25
Exercise price range, options exercisable (in shares) | shares	627
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 75.28
$80.01–$100.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	80.01
Exercise price, high end of range (in dollars per share)	$ 100
Exercise price range, options outstanding (in shares) | shares	3,791
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	7 years 10 months 6 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 89.21
Exercise price range, options exercisable (in shares) | shares	1,357
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 89.45
$100.01–$120.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	100.01
Exercise price, high end of range (in dollars per share)	$ 120
Exercise price range, options outstanding (in shares) | shares	972
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	6 years 9 months 18 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 109.28
Exercise price range, options exercisable (in shares) | shares	622
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 109.15
$120.01–$140.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	120.01
Exercise price, high end of range (in dollars per share)	$ 140.00
Exercise price range, options outstanding (in shares) | shares	1,138
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	7 years 4 months 6 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 130.20
Exercise price range, options exercisable (in shares) | shares	732
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 129.98
$140.01–$160.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	140.01
Exercise price, high end of range (in dollars per share)	$ 160.00
Exercise price range, options outstanding (in shares) | shares	1,496
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	9 years 10 months 10 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 155.57
Exercise price range, options exercisable (in shares) | shares	10
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 155.57
$160.01–$163.74
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	160.01
Exercise price, high end of range (in dollars per share)	$ 163.74
Exercise price range, options outstanding (in shares) | shares	600
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	9 years 3 months
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 162.94
Exercise price range, options exercisable (in shares) | shares	76
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 162.94