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Summary of Restricted Stock Unit and Performance Stock Unit Activity (Detail) - Restricted Stock Units and Performance Stock Units
$ in Thousands
 3 Months Ended
Mar. 31, 2018
USD ($)
shares
Options Outstanding  
Restricted and performance stock units outstanding at December 31, 2017 505,235
Granted 319,701
Exercised (90,691)
Forfeited/cancelled (31,169)
Restricted stock units outstanding at March 31, 2018 703,076
Vested and expected to vest at March 31, 2018 639,530 [1]
Weighted-Average Remaining Contractual Term (in years)  
Restricted stock units outstanding at March 31, 2018 4 years 22 days
Vested and expected to vest at March 31, 2018 3 years 9 months [1]
Aggregate Intrinsic Value  
Restricted stock units outstanding at March 31, 2018 | $ $ 25,437
Vested and expected to vest at March 31, 2018 | $ $ 23,138 [1]
[1] Represents the number of vested restricted stock units as of March 31, 2018 plus the number of unvested restricted stock units expected to vest as of March 31, 2018 based on the unvested outstanding restricted stock units at March 31, 2018 adjusted for estimated forfeiture rates of 8% for awards granted to non-executive level employees and 3% for awards granted to executive level employees.