Stock-based Compensation Expense and Share Repurchase - Stock Options Outstanding and Exercisable (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price range, options outstanding (in shares) | shares	8,702
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	7 years 3 months 11 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 124.11
Exercise price range, options exercisable (in shares) | shares	4,412
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 100.04
$29.07–$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)	29.07
Exercise price, high end of range (in dollars per share)	$ 40
Exercise price range, options outstanding (in shares) | shares	252
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	1 year 8 months 1 day
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 35.87
Exercise price range, options exercisable (in shares) | shares	252
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 35.87
$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	437
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	3 years 2 months 12 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 50.23
Exercise price range, options exercisable (in shares) | shares	437
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 50.23
$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	525
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	5 years 7 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 74.83
Exercise price range, options exercisable (in shares) | shares	516
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 74.82
$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	2,481
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	6 years 11 months 12 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 89.20
Exercise price range, options exercisable (in shares) | shares	1,315
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 89.81
$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	622
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	5 years 10 months 17 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 109.32
Exercise price range, options exercisable (in shares) | shares	614
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 109.24
$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	773
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	6 years 4 months 10 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 130.20
Exercise price range, options exercisable (in shares) | shares	653
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 130.24
$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	1,287
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	8 years 9 months 26 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 155.51
Exercise price range, options exercisable (in shares) | shares	333
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 155.35
$160.01–$180.00
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)	$ 180.00
Exercise price range, options outstanding (in shares) | shares	502
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	8 years 3 months 18 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 162.94
Exercise price range, options exercisable (in shares) | shares	177
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 162.95
$180.01–$187.53
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	180.01
Exercise price, high end of range (in dollars per share)	$ 181.60
Exercise price range, options outstanding (in shares) | shares	1,823
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	9 years 7 months 24 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 185.29
Exercise price range, options exercisable (in shares) | shares	115
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 182.72