Assumptions Used to Estimate Fair Value of Employee Stock Purchase Plan (Detail)
|
12 Months Ended |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Expected dividend yield |
0.00%
|
[1] |
0.00%
|
0.00%
|
| Expected volatility, Minimum |
38.00%
|
[1] |
33.00%
|
33.00%
|
| Expected volatility, Maximum |
49.00%
|
[1] |
49.00%
|
52.00%
|
| Risk-free interest rate, Minimum |
0.50%
|
[1] |
0.20%
|
0.10%
|
| Risk-free interest rate, Maximum |
2.40%
|
[1] |
2.40%
|
2.50%
|
| Expected forfeiture |
|
|
10.00%
|
10.00%
|
| Contractual term of up to |
10 years
|
[1] |
10 years
|
10 years
|
| Employee stock purchase plan |
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Expected dividend yield |
0.00%
|
|
0.00%
|
0.00%
|
| Expected volatility, Minimum |
29.00%
|
|
35.00%
|
29.00%
|
| Expected volatility, Maximum |
57.00%
|
|
36.00%
|
52.00%
|
| Risk-free interest rate, Minimum |
0.30%
|
|
0.10%
|
0.10%
|
| Risk-free interest rate, Maximum |
0.50%
|
|
0.30%
|
0.20%
|
| Expected forfeiture |
0.00%
|
|
0.00%
|
0.00%
|
| Contractual term of up to |
24 months
|
|
24 months
|
24 months
|
|
|