Stock-based Compensation Expense - Stock Options Outstanding and Exercisable (Details) shares in Thousands	6 Months Ended
	Jun. 30, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price range, options outstanding (in shares) | shares	11,536
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	7 years 2 months 16 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 86.12
Exercise price range, options exercisable (in shares) | shares	6,371
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 77.74
$18.93–$20.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Exercise price, low end of range (in dollars per share)	18.93
Exercise price, high end of range (in dollars per share)	$ 20.00
Exercise price range, options outstanding (in shares) | shares	129
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	7 months 10 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 18.93
Exercise price range, options exercisable (in shares) | shares	129
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 18.93
$20.01–$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)	20.01
Exercise price, high end of range (in dollars per share)	$ 40
Exercise price range, options outstanding (in shares) | shares	943
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	2 years 6 months 26 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 34.74
Exercise price range, options exercisable (in shares) | shares	943
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 34.74
$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	1,233
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	5 years 1 month 24 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 48.58
Exercise price range, options exercisable (in shares) | shares	1,233
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 48.58
$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	1,042
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	6 years 8 months 9 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 75.83
Exercise price range, options exercisable (in shares) | shares	784
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 75.63
$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	5,336
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	8 years 5 months 12 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 89.52
Exercise price range, options exercisable (in shares) | shares	1,733
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 89.89
$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	1,437
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	7 years 6 months 22 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 109.35
Exercise price range, options exercisable (in shares) | shares	786
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 109.27
$120.01–$131.89
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)	$ 131.89
Exercise price range, options outstanding (in shares) | shares	1,416
Exercise price range, options outstanding, weighted-average remaining contractual life (in years)	8 years 11 days
Exercise price range, options outstanding, weighted-average exercise price (in dollars per share)	$ 130.34
Exercise price range, options exercisable (in shares) | shares	763
Exercise price range, options exercisable, weighted-average exercise price (in dollars per share)	$ 130.00