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Common Stock - Additional Information (Detail) $ / shares in Units, $ in Millions					12 Months Ended
	Apr. 09, 2019 shares	Sep. 11, 2018 $ / shares shares	Aug. 14, 2018 USD ($) $ / shares shares	Aug. 08, 2018 shares	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 30, 2018 $ / shares shares	Jun. 28, 2018 shares
Class of Warrant or Right [Line Items]
Warrants term					5 years
Warrants of common stock exercise price | $ / shares					$ 0.004
Maximum percentage of stock pertaining to restrictions					24.90%
Extended term of outstanding warrants expiration period					5 years
Warrants of common stock expiration date					Sep. 30, 2023
Warrants to purchase shares of common stock							250,000
Common stock, stock split					Effected a 2.5-for-1 stock split
Stock split ratio				2.5
Common stock, shares authorized				125,000,000	125,000,000	125,000,000
Preferred stock, shares authorized				5,000,000	5,000,000	5,000,000
Stock issued during period, shares, new issues		1,344,500
Common stock, no par value | $ / shares					$ 0	$ 0
Common stock, warrants issued					3,600,953	10,614,990
2018 Equity Incentive Plan [Member]
Class of Warrant or Right [Line Items]
Increase in number of shares authorized for issuance	1,000,000
Common stock, shares authorized	3,500,000
IPO [Member]
Class of Warrant or Right [Line Items]
Stock issued during period, shares, new issues			9,630,000
Common stock, no par value | $ / shares
Shares issued, price per share | $ / shares			$ 12.00
Gross proceeds of initial public offering | $			$ 115.6		$ 124.2
Net proceeds from initial public offering | $					111.7
Underwriting discounts and commissions | $					8.7
Offering costs | $					$ 3.6
Underwriter Options [Member]
Class of Warrant or Right [Line Items]
Common stock, warrants issued			1,444,500
Firm Shares and Option Shares [Member]
Class of Warrant or Right [Line Items]
Shares issued, price per share | $ / shares		$ 12.00
Purchased Directly From Company [Member]
Class of Warrant or Right [Line Items]
Stock issued during period, shares, new issues		723,985
Purchased Directly From Selling Shareholders [Member]
Class of Warrant or Right [Line Items]
Stock issued during period, shares, new issues		620,515

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