Stock-Based Compensation - Schedule of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Original Stock Option Plan [Member]
Stock options
Shares, Beginning Balance	1,789,750
Shares, Granted	0	0
Shares, Exercised	(757,318)
Shares, Cancelled	(80)
Shares, Ending Balance	1,032,352		1,789,750
Shares, Vested and expected to vest	986,020
Shares, Vested and exercisable	945,951
Weighted-average exercise price
Weighted-average exercise price, Beginning Balance	$ 3.62
Weighted-average exercise price, Exercised	3.17
Weighted-average exercise price, Cancelled	4.72
Weighted-average exercise price, Ending Balance	3.93		$ 3.62
Weighted-average exercise price, Vested and expected to vest	3.91
Weighted-average exercise price, Vested and exercisable	$ 3.72
Weighted-average remaining contractual term (years)
Weighted-average remaining contractual term	4 years 3 months 18 days		3 years 9 months 18 days
Weighted-average remaining contractual term, Vested and expected to vest	4 years 3 months 18 days
Weighted-average remaining contractual term, Vested and exercisable	4 years 2 months 12 days
Aggregate intrinsic value
Aggregate intrinsic value	$ 13,660		$ 25,077
Aggregate intrinsic value, Vested and expected to vest	13,618
Aggregate intrinsic value, Vested and exercisable	$ 13,200
2018 Equity Incentive Plan [Member] | Time-based Stock Options [Member]
Stock options
Shares, Beginning Balance	3,909,559
Shares, Exercised	(471,211)
Shares, Forfeited	(33,291)
Shares, Cancelled	(36,414)
Shares, Ending Balance	3,368,643		3,909,559
Shares, Vested and expected to vest	3,360,695
Shares, Vested and exercisable	2,902,957
Weighted-average exercise price
Weighted-average exercise price, Beginning Balance	$ 15.25
Weighted-average exercise price, Exercised	7.76
Weighted-average exercise price, Forfeited	8.46
Weighted-average exercise price, Cancelled	42.61
Weighted-average exercise price, Ending Balance	16.02		$ 15.25
Weighted-average exercise price, Vested and expected to vest	15.87
Weighted-average exercise price, Vested and exercisable	$ 13.77
Weighted-average remaining contractual term (years)
Weighted-average remaining contractual term	7 years 2 months 12 days		7 years 4 months 24 days
Weighted-average remaining contractual term, Vested and expected to vest	7 years 2 months 12 days
Weighted-average remaining contractual term, Vested and exercisable	7 years 2 months 12 days
Aggregate intrinsic value
Aggregate intrinsic value	$ 43,421		$ 1,700,194
Aggregate intrinsic value, Vested and expected to vest	43,213
Aggregate intrinsic value, Vested and exercisable	$ 38,916