Stockholders' Deficit - Schedule of Stock Option Activity (Detail) - 2016 Plan - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Options outstanding beginning balance, shares		252,850	0
Granted, shares		1,452,550	260,725
Forfeited / Cancelled, shares		(43,650)	(7,875)
Options outstanding ending balance, shares	1,661,750	1,661,750	252,850	0
Options vested and exercisable, shares	493,423	493,423
Options vested and expected to vest, shares	1,661,750	1,661,750
Weighted- average exercise price
Options outstanding, beginning balance (usd per share)		$ 40.16	$ 0.00
Granted (usd per share)		7.11	40.16
Forfeited / Cancelled (usd per share)		0.00	40.00
Options outstanding, beginning balance (usd per share)	$ 11.96	11.96	$ 40.16	$ 0.00
Options vested and exercisable (usd per share)	15.64	15.64
Options vested and expected to vest (usd per share)	$ 11.96	$ 11.96
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted-average contractual life, Options outstanding	9 years 1 month 15 days		9 years 4 months 28 days	0 years
Weighted-average contractual life, Options granted		10 years	10 years
Weighted-average contractual life, Options vested and exercisable		9 years 5 days
Weighted-average contractual life, Options vested and expected to vest		9 years 1 month 15 days
Aggregate intrinsic value, Options outstanding		$ 37	$ 0
Aggregate intrinsic value, Options granted		91	37
Aggregate intrinsic value, Options outstanding	$ 75	75	$ 37	$ 0
Aggregate intrinsic value, vested and exercisable	2	2
Aggregate intrinsic value, Vested and expected to vest	$ 75	$ 75