Summary of Option Activity (Detail) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) $ / shares shares
Options Outstanding
Options outstanding at December 31, 2018	998,226
Granted	31,498
Exercised	(1,893)
Forfeited/expired/cancelled	0
Options outstanding at March 31, 2019	1,027,831
Options exercisable at March 31, 2019	540,600
Vested and expected to vest at March 31, 2019	985,138	[1]
Weighted-Average Exercise Price Per Share
Options outstanding at December 31, 2018 | $ / shares	$ 27.54
Granted | $ / shares	59.52
Exercised | $ / shares	22.35
Forfeited/expired/cancelled | $ / shares	0
Options outstanding at March 31, 2019 | $ / shares	28.53
Options exercisable at March 31, 2019 | $ / shares	$ 21.66
Weighted-Average Remaining Contractual Term (in years)
Options outstanding at March 31, 2019	7 years 14 days
Options exercisable at March 31, 2019	5 years 6 months 14 days
Vested and expected to vest at March 31, 2019	6 years 11 months 15 days	[1]
Aggregate Intrinsic Value
Options outstanding at March 31, 2019 | $	$ 31,469
Options exercisable at March 31, 2019 | $	20,231
Vested and expected to vest at March 31, 2019 | $	$ 30,511	[1]

[1] Represents the number of vested options as of March 31, 2019 plus the number of unvested options expected to vest as of March 31, 2019 based on the unvested outstanding options 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.