Share-Based Payments - Summary of Company's Stock Option Activity (Details)	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Stock Options, Outstanding, Beginning balance (in shares) | shares	5,577,562
Number of Stock Options, Granted (in shares) | shares	1,293,020
Number of Stock Options, Exercised (in shares) | shares	(1,078,290)
Number of Stock Options, Forfeited/Expired (in shares) | shares	(306,978)
Number of Stock Options, Outstanding, Ending balance (in shares) | shares	5,485,314
Number of Stock Options, Exercisable (in shares) | shares	2,774,270
Number of Stock Options, Vested and expected to vest (in shares) | shares	5,485,314
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-Average Exercise Price, Outstanding, Beginning balance (in usd per share) | $ / shares	$ 49.58
Weighted-Average Exercise Price, Granted (in usd per share) | $ / shares	78.35
Weighted-Average Exercise Price, Exercised (in usd per share) | $ / shares	24.13
Weighted-Average Exercise Price, Forfeited/Expired (in usd per share) | $ / shares	76.15
Weighted-Average Exercise Price, Outstanding, Ending balance (in usd per share) | $ / shares	59.88
Weighted-Average Exercise Price, Exercisable (in usd per share) | $ / shares	54.67
Weighted-Average Exercise Price, Vested and expected to vest (in usd per share) | $ / shares	$ 59.88