Equity Incentive Plans - Summary of Activities under Its Equity Incentive Plans (Detail)	3 Months Ended
	Mar. 31, 2018 USD ($) $ / shares shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares Available for Grant, Outstanding Beginning Balance	2,028,880
Available for Grant, Shares authorized	1,940,000
Shares Available for Grant, Granted	(1,964,034)
Shares Available for Grant, Exercised	79,585
Shares Available for Grant, Forfeited and expired	33,363
Shares Available for Grant, Outstanding Ending Balance	2,117,794
Shares, Options Outstanding, Beginning Balance	10,203,571
Shares, Options Outstanding, authorized	0
Shares, Options Outstanding, Granted	1,785,700
Shares, Options Outstanding, Exercised	(172,221)
Shares, Options Outstanding, Forfeited and expired	(33,363)
Shares, Options Outstanding, Ending Balance	11,783,687
Shares, Vested and expected to vest, net of estimated forfeiture at March 31, 2018	11,422,322
Shares, Exercisable at March 31, 2018	7,513,183
Weighted Average Exercise Price, Options Outstanding, Beginning Balance | $ / shares	$ 7.68
Weighted Average Exercise Price, Options Outstanding, Shares authorized | $ / shares	0
Weighted Average Exercise Price, Options Outstanding, Granted | $ / shares	9.33
Weighted Average Exercise Price, Options Outstanding, Exercised | $ / shares	6.55
Weighted Average Exercise Price, Options Outstanding, Forfeited and expired | $ / shares	6.23
Weighted Average Exercise Price, Options Outstanding, Ending Balance | $ / shares	7.95
Weighted Average Exercise Price, Vested and expected to vest, net of estimated forfeiture at March 31, 2018 | $ / shares	7.95
Weighted Average Exercise Price, Exercisable at March 31, 2018 | $ / shares	$ 8.26
Options Outstanding, Weighted Average Remaining Contractual Term	6 years 6 months 25 days
Weighted Average Remaining Contractual Term, Vested and expected to vest, net of estimated forfeiture at March 31, 2018	6 years 5 months 23 days
Weighted Average Remaining Contractual Term, Exercisable at March 31, 2018	5 years 1 month 16 days
Aggregate Intrinsic Value, Outstanding, Ending Balance | $	$ 67,738,549
Aggregate Intrinsic Value, Vested and expected to vest, net of estimated forfeiture at March 31, 2018 | $	65,647,643
Aggregate Intrinsic Value, Exercisable at March 31, 2018 | $	$ 41,281,567