Share-based Payments - Summary of Black-Scholes Option-Pricing Models (Details) - USD ($) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Bottom Of Range [Member] | |||
| Disclosure Of Share Based Payments [Line Items] | |||
| Expected volatility (%) | 32.00% | 32.00% | 37.90% |
| Risk-free interest rate (%) | 2.40% | 1.40% | 0.80% |
| Expected life of share options (years) | 2 years 4 months 24 days | 2 years 4 months 24 days | 2 years 6 months |
| Weighted-average share price (US$) | $ 123.13 | $ 50.70 | $ 41.20 |
| Top of range | |||
| Disclosure Of Share Based Payments [Line Items] | |||
| Expected volatility (%) | 34.70% | 43.50% | 45.80% |
| Risk-free interest rate (%) | 2.90% | 2.00% | 1.80% |
| Expected life of share options (years) | 4 years 4 months 24 days | 4 years 4 months 24 days | 5 years |
| Weighted-average share price (US$) | $ 189.52 | $ 90.65 | $ 44.40 |