Stock-Based Compensation - Schedule of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Original Stock Option Plan [Member]
Stock options
Shares, Beginning Balance	3,014,004
Shares, Granted	0
Shares, Exercised	(1,076,156)
Shares, Forfeited	(81,658)
Shares, Cancelled	(66,440)
Shares, Ending Balance	1,789,750	3,014,004
Shares, Vested and expected to vest	1,784,519
Shares, Vested and exercisable	1,731,626
Weighted-average exercise price
Weighted-average exercise price, Beginning Balance	$ 3.04
Weighted-average exercise price, Exercised	1.80
Weighted-average exercise price, Forfeited	4.59
Weighted-average exercise price, Cancelled	3.81
Weighted-average exercise price, Ending Balance	3.62	$ 3.04
Weighted-average exercise price, Vested and expected to vest	3.61
Weighted-average exercise price, Vested and exercisable	$ 3.48
Weighted-average remaining contractual term (years)
Weighted-average remaining contractual term	3 years 9 months 7 days	5 years 9 months 18 days
Weighted-average remaining contractual term, Vested and expected to vest	3 years 9 months 3 days
Weighted-average remaining contractual term, Vested and exercisable	3 years 7 months 24 days
Aggregate intrinsic value
Aggregate intrinsic value	$ 44,108
Aggregate intrinsic value	25,077	$ 44,108
Aggregate intrinsic value, Vested and expected to vest	25,020
Aggregate intrinsic value, Vested and exercisable	$ 24,449
Time-based Stock Options [Member] | 2018 Equity Incentive Plan [Member]
Stock options
Shares, Beginning Balance	5,307,130
Shares, Granted
Shares, Exercised	(703,393)
Shares, Forfeited	(468,096)
Shares, Cancelled	(226,082)
Shares, Ending Balance	3,909,559	5,307,130
Shares, Vested and expected to vest	3,840,493
Shares, Vested and exercisable	3,142,175
Weighted-average exercise price
Weighted-average exercise price, Beginning Balance	$ 14.04
Weighted-average exercise price, Exercised	7.76
Weighted-average exercise price, Forfeited	13.73
Weighted-average exercise price, Cancelled	13.20
Weighted-average exercise price, Ending Balance	15.25	$ 14.04
Weighted-average exercise price, Vested and expected to vest	15.10
Weighted-average exercise price, Vested and exercisable	$ 13.16
Weighted-average remaining contractual term (years)
Weighted-average remaining contractual term	7 years 4 months 24 days	8 years 4 months 24 days
Weighted-average remaining contractual term, Vested and expected to vest	7 years 4 months 24 days
Weighted-average remaining contractual term, Vested and exercisable	13 years 2 months 12 days
Aggregate intrinsic value
Aggregate intrinsic value	$ 44,297
Aggregate intrinsic value	1,700,194	$ 44,297
Aggregate intrinsic value, Vested and expected to vest	1,675,302
Aggregate intrinsic value, Vested and exercisable	$ 1,423,560
Performance-based Stock Options [Member] | 2018 Equity Incentive Plan [Member]
Stock options
Shares, Beginning Balance	520,000
Shares, Exercised	(520,000)
Shares, Ending Balance		520,000
Weighted-average exercise price
Weighted-average exercise price, Beginning Balance	$ 7.76
Weighted-average exercise price, Exercised	$ 7.76
Weighted-average exercise price, Ending Balance		$ 7.76
Weighted-average remaining contractual term (years)
Weighted-average remaining contractual term		8 years 4 months 24 days
Aggregate intrinsic value
Aggregate intrinsic value	$ 4,872
Aggregate intrinsic value		$ 4,872