Summary of Restricted Stock Unit and Performance Stock Unit Activity (Detail) - Restricted Stock Units and Performance Stock Units $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) shares
Options Outstanding
Restricted and performance stock units outstanding at December 31, 2017	505,235
Granted	367,961
Vested	(115,295)
Forfeited/cancelled	(40,905)
Restricted stock units outstanding at March 31, 2018	716,996
Vested and expected to vest at March 31, 2018	654,423	[1]
Weighted-Average Remaining Contractual Term (in years)
Restricted stock units outstanding at June 30, 2018	3 years 11 months 19 days
Vested and expected to vest at June 30, 2018	3 years 7 months 6 days	[1]
Aggregate Intrinsic Value
Restricted stock units outstanding at June 30, 2018 | $	$ 33,727
Vested and expected to vest at June 30, 2018 | $	$ 30,784	[1]

[1] Represents the number of unvested restricted stock units expected to vest as of June 30, 2018 based on the unvested outstanding restricted stock units at June 30, 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.