Share-Based Compensation - Stock Option Activity (Details) shares in Thousands	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Number of Options (in thousands)
Outstanding beginning balance (in shares) | shares	3,610
Granted (in shares) | shares	493
Exercised (in shares) | shares	(172)
Outstanding ending balance (in shares) | shares	3,931
Weighted Average Exercise Price per Option
Outstanding beginning balance (in dollars per share) | $ / shares	$ 46.44
Granted (in dollars per share) | $ / shares	76.16
Exercised (in dollars per share) | $ / shares	29.07
Outstanding ending balance (in dollars per share) | $ / shares	$ 50.93