Ordinary Shares, Convertible Preferred C Shares and Shareholders' Deficit - Additional Information (Detail) - USD ($)										12 Months Ended
	Oct. 05, 2018	Jun. 07, 2018	Jun. 05, 2018	Mar. 15, 2018	Mar. 01, 2018	Nov. 02, 2017	Sep. 21, 2017	Aug. 16, 2017	Jul. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Percentage of fully diluted shares		5.00%
Stock issued during period, shares, stock options exercised											1,288
Gross proceeds from preferred shares										$ 56,849,594	$ 16,854,653
Conversion of note payable into convertible preferred C shares, shares						238,579
Preferred share conversion value		$ 664,718								1,806,512	191,963
Conversion of note payable into convertible preferred C shares						$ 2,500,000				$ 120,520,391
Preferred shares, purchase			927,594				695,696
Preferred shares, exercise price			$ 10.48				$ 10.48			$ 2.70
Accretion of warrants issued in connection with convertible preferred shares							$ 1,660,500			$ (1,045,500)	(615,000)
Convertible note inducement expense											553,500
Change in fair value of warrant liability										1,514,775	465,633
Warrant liability			$ 4,194,408								$ 2,679,633
Preferred shares, value			$ 9,720,000							$ 9,720,000
Vector Neurosciences Inc [Member]
Number of shares issued as initial merger consideration	225,000
Period of shares issued as initial merger consideration	18 months
Vector Neurosciences Inc [Member] | Issued at Closing of Merger [Member]
Number of shares issued as initial merger consideration	202,500
Vector Neurosciences Inc [Member] | Issued Following Closing of Merger [Member]
Number of shares issued as initial merger consideration	22,500
Restricted Shares [Member]
Ordinary shares, offering price		$ 15.00
Ordinary shares		1,306,348								1,306,348
Percentage of fully diluted shares		5.00%
Ordinary shares [Member]
Ordinary shares, issued		5,000,000			550,162
Ordinary shares, offering price		$ 15.00
Proceeds from issuance initial public offering		$ 75,000,000
Offering costs		$ 9,807,622								$ 4,115,843
Percentage of fully diluted shares					3.00%
Stock issued during period, shares, stock options exercised									1,288		1,288
Conversion of note payable into convertible preferred C shares, shares		11,501,432								11,501,432
Conversion of note payable into convertible preferred C shares										$ 446
Ordinary shares [Member] | Research Agreement [Member]
Ordinary shares, issued								6,441
Ordinary shares [Member] | Restricted Shares [Member]
Ordinary shares												867,935
Preferred Shares [Member]
Ordinary shares, issued							715,737			5,425,124
Ordinary shares, offering price							$ 10.48			$ 10.48
Offering costs										$ 690,473	$ 98,804
Gross proceeds from preferred shares										56,849,611	$ 16,854,656
Conversion of note payable into convertible preferred C shares, shares						238,579
Conversion rate of note payable into convertible preferred shares						10.48
Preferred Shares [Member] | Issued at Closing of Merger [Member]
Ordinary shares, issued											9,739
Ordinary shares, offering price											$ 20.96
Preferred Shares [Member] | Issued Following Closing of Merger [Member]
Ordinary shares, issued											1,598,418
Ordinary shares, offering price											$ 10.48
Convertible Preferred C Shares [Member]
Offering costs										$ 690,475
Conversion of note payable into convertible preferred C shares, shares										(11,501,432)	238,579
Conversion of note payable into convertible preferred C shares										$ (120,520,391)	$ 2,500,000
Preferred shares, purchase										927,594
Convertible Preferred C Shares [Member] | License Agreement [Member]
Ordinary shares, issued				13,360						13,360
Convertible Preferred C Shares [Member] | Payments In Lieu [Member]
Ordinary shares, issued										129,419
Shares issued, value										$ 1,355,097