Share-Based Compensation - Schedule of Estimated Fair Value of Share-Based Awards on Respective Grant Dates using Binomial Option Pricing Model (Detail) - $ / shares
|
12 Months Ended |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Risk-free interest rates, Minimum |
2.30%
|
1.70%
|
|
| Risk-free interest rates, Maximum |
2.44%
|
1.75%
|
|
| Expected volatility |
|
63.00%
|
|
| Expected volatility, Minimum |
57.00%
|
|
|
| Expected volatility, Maximum |
60.00%
|
|
|
| Expected dividend yield |
0.00%
|
0.00%
|
|
| Weighted average fair value per option granted |
$ 30.23
|
$ 14.62
|
$ 0.00
|
| Minimum [Member] |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Fair value of ordinary share |
$ 45.36
|
$ 23.76
|
|
| Expected exercise multiple |
2.2
|
2.2
|
|
| Weighted average fair value per option granted |
$ 27.05
|
$ 14.12
|
|
| Maximum [Member] |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Fair value of ordinary share |
$ 54.84
|
$ 24.88
|
|
| Expected exercise multiple |
2.8
|
2.8
|
|
| Weighted average fair value per option granted |
$ 33.73
|
$ 15.26
|
|