Stock-Based Compensation - Summary of Options Outstanding and Weighted Average Exercise Price (Detail) - USD ($)	12 Months Ended			33 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Shares, Options Outstanding, Beginning balance	2,987,729	1,953,480	69,766
Number of Shares, Granted	1,538,342	1,294,711	1,883,714
Number of Shares, Exercised	(4,320)	0	0	0
Number of Shares, Forfeited	(222,949)	(260,462)	0
Number of Shares, Options Outstanding, Ending balance	4,298,802	2,987,729	1,953,480	2,987,729
Number of Shares, Vested and exercisable	1,733,673	683,070	23,255	683,070
Weighted Average Exercise Price, Options Outstanding	$ 7.46	$ 7.95	$ 0.22
Weighted Average Exercise Price, Granted	9.03	6.87	8.24
Weighted Average Exercise Price, Exercised	6.26	0	0
Weighted Average Exercise Price, Forfeited	6.61	8.18	0
Weighted Average Exercise Price, Options Outstanding	8.07	7.46	7.95	$ 7.46
Weighted Average Exercise Price, Vested and exercisable	$ 7.65	$ 7.71	$ 0.22	$ 7.71
Weighted Average Remaining Contractual Life, Options Outstanding	8 years 3 months 25 days	8 years 9 months 25 days	8 years 2 months 4 days
Weighted Average Remaining Contractual Life, Vested and exercisable	7 years 11 months 1 day	8 years 5 months 19 days	8 years 8 months 15 days
Weighted Average Remaining Contractual Life, Granted		9 years 2 months 8 days
Aggregate Intrinsic Value, Options Outstanding	$ 8,174,686	$ 837,036	$ 780,500	$ 837,036
Aggregate Intrinsic Value, Vested and exercisable	$ 3,865,036	$ 253,969	$ 567,000	$ 253,969