Stock-Based Compensation - Exercise Price for Stock Options Outstanding and Exercisable (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Exercise prices for stock options outstanding and exercisable
Number of stock options outstanding (in shares)	8,969,886
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 40.34
Stock options
Exercise prices for stock options outstanding and exercisable
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 80.00
Number of stock options outstanding (in shares)	14,202,039	8,847,734	7,923,009	6,845,685
Options Outstanding, Weighted-Average Remaining Contractual Life	7 years 5 months 12 days
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 42.08	$ 43.90	$ 36.21	$ 31.13
Number of stock options exercisable	1,781,153	1,772,608	1,892,809
Options Exercisable, Weighted-Average Remaining Contractual Life	4 years 3 months
Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 41.41	$ 35.13	$ 29.97
Stock options | Range of Exercise Prices $00.00 - $10.00
Exercise prices for stock options outstanding and exercisable
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 10.00
Number of stock options outstanding (in shares)	18,800
Options Outstanding, Weighted-Average Remaining Contractual Life	3 months
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 6.34
Number of stock options exercisable	18,800
Options Exercisable, Weighted-Average Remaining Contractual Life	3 months
Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 6.34
Stock options | Range Of Exercise Prices $10.01 - $20.00
Exercise prices for stock options outstanding and exercisable
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	10.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 20.00
Number of stock options outstanding (in shares)	621,537
Options Outstanding, Weighted-Average Remaining Contractual Life	1 year 5 months 27 days
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 15.37
Number of stock options exercisable	21,537
Options Exercisable, Weighted-Average Remaining Contractual Life	1 year 3 months 29 days
Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 15.07
Stock options | Range of Exercise Prices $20.01 - $30.00
Exercise prices for stock options outstanding and exercisable
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	20.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 30.00
Number of stock options outstanding (in shares)	1,284,883
Options Outstanding, Weighted-Average Remaining Contractual Life	2 years 8 months 23 days
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 27.61
Number of stock options exercisable	744,883
Options Exercisable, Weighted-Average Remaining Contractual Life	2 years 8 months 19 days
Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 27.40
Stock options | Range of Exercise Prices $30.01 - $40.00
Exercise prices for stock options outstanding and exercisable
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	30.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 40.00
Number of stock options outstanding (in shares)	6,683,886
Options Outstanding, Weighted-Average Remaining Contractual Life	8 years 8 months 23 days
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 35.78
Number of stock options exercisable	223,131
Options Exercisable, Weighted-Average Remaining Contractual Life	3 years 8 months 16 days
Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 34.83
Stock options | Range of Exercise Prices $40.01 - $50.00
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)	$ 50.00
Number of stock options outstanding (in shares)	1,765,405
Options Outstanding, Weighted-Average Remaining Contractual Life	8 years 6 months 7 days
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 47.49
Number of stock options exercisable	143,700
Options Exercisable, Weighted-Average Remaining Contractual Life	6 years 6 months 15 days
Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 46.54
Stock options | Range of Exercise Prices $50.01 - $60.00
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)	$ 60.00
Number of stock options outstanding (in shares)	2,456,378
Options Outstanding, Weighted-Average Remaining Contractual Life	7 years 4 months 2 days
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 57.54
Number of stock options exercisable	343,752
Options Exercisable, Weighted-Average Remaining Contractual Life	6 years 4 days
Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 57.05
Stock options | Range of Exercise Prices $60.01 - $70.00
Exercise prices for stock options outstanding and exercisable
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	60.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 70.00
Number of stock options outstanding (in shares)	1,351,150
Options Outstanding, Weighted-Average Remaining Contractual Life	7 years 4 months 17 days
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 64.17
Number of stock options exercisable	265,350
Options Exercisable, Weighted-Average Remaining Contractual Life	6 years 2 months 23 days
Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 65.47
Stock options | Range of Exercise Prices $70.01 - $80.00
Exercise prices for stock options outstanding and exercisable
Exercise prices, outstanding stock option awards, low end of range (in dollars per share)	70.01
Exercise prices, outstanding stock option awards, high end of range (in dollars per share)	$ 80.00
Number of stock options outstanding (in shares)	20,000
Options Outstanding, Weighted-Average Remaining Contractual Life	1 year
Options Outstanding, Weighted-Average Exercise Price (in dollars per share)	$ 72.89
Number of stock options exercisable	20,000
Options Exercisable, Weighted-Average Remaining Contractual Life	1 year
Options Exercisable, Weighted-Average Exercise Price (in dollars per share)	$ 72.89