Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units (RSUs) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) shares
Options Outstanding
Unvested at December 31, 2018	705,413
Awarded	147,474
Vested	(154,837)
Forfeited/expired/cancelled	(17,501)
Unvested at March 31, 2019	680,549
Vested and expected to vest at March 31, 2019	622,851	[1]
Weighted-Average Remaining Contractual Term (in years)
Unvested at March 31, 2019	3 years 10 months 17 days
Vested and expected to vest at March 31, 2019	3 years 6 months 14 days	[1]
Aggregate Intrinsic Value
Unvested at March 31, 2019 | $	$ 40,207
Vested and expected to vest at March 31, 2019 | $	$ 36,798	[1]

[1] Represents the number of vested RSUs units as of March 31, 2019 plus the number of unvested RSUs expected to vest as of March 31, 2019 based on the unvested outstanding RSUs at March 31, 2019 adjusted for estimated forfeiture rates of 8% for awards granted to non-executive level employees and 3% for awards granted to executive level employees.