Stock-Based Compensation - Summary of Stock-Based Compensation Expense by Award Type Recognized (Detail) - USD ($) $ in Thousands |
3 Months Ended | |
---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
Total Stock-based compensation expense | $ 15,817 | $ 6,208 |
Stock Options [Member] | ||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
Total Stock-based compensation expense | 15,381 | 6,033 |
Restricted Stock Units [Member] | ||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
Total Stock-based compensation expense | 168 | 100 |
Employee Stock Purchase Plan [Member] | ||
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
Total Stock-based compensation expense | $ 268 | $ 75 |