Nature of Organization and Operations - Additional Information (Detail)				9 Months Ended
	Jul. 02, 2018 USD ($) shares	Jun. 28, 2018 shares	Mar. 15, 2017 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 $ / shares shares	Mar. 14, 2017 shares	Mar. 10, 2017 $ / shares shares	Mar. 03, 2017 $ / shares shares
Class Of Stock [Line Items]
Common stock, shares authorized				300,000,000		300,000,000		300,000,000	100,000,000
Common stock, par value | $ / shares				$ 0.0001		$ 0.0001		$ 0.0001	$ 0.0001
Preferred stock, shares authorized				10,000,000		10,000,000		10,000,000	10,000,000
Preferred stock, par value | $ / shares				$ 0.0001		$ 0.0001		$ 0.0001	$ 0.0001
Capital stock conversion basis ratio			2.3336572
Common stock, shares outstanding				40,588,004		27,070,038
Net proceeds of common stock issued to private placement | $				$ 48,119,027
Warrants issued to purchase common stock, exercise price | $ / shares				$ 5.00		$ 5.00
Payments of stock issuance cost | $				$ 3,502,543	$ 3,084,385
Proceeds from sale of common stock | $				$ 51,621,570	$ 40,247,775
2018 Public Offering [Member]
Class Of Stock [Line Items]
Common stock issued to private placement		11,688,000
Payments of stock issuance cost | $	$ 3,500,000
Proceeds from sale of common stock | $	$ 48,100,000
Underwriters’ Exercise of Option [Member]
Class Of Stock [Line Items]
Common stock issued to private placement	1,720,200
Minimum [Member]
Class Of Stock [Line Items]
Percentage of Interest owned in the combined enterprise			50.00%
Common Stock [Member]
Class Of Stock [Line Items]
Common stock issued to private placement				13,408,200
Net proceeds of common stock issued to private placement | $				$ 1,341
Zeta Acquisition Corp. II [Member]
Class Of Stock [Line Items]
Number of shares surrendered for cancellation			4,000,000
Common stock, shares outstanding							5,000,000
Issuance of warrants term			3 years
Number of warrants issued to purchase common stock			317,562
Warrants issued to purchase common stock, exercise price | $ / shares			$ 5.00
Zeta Acquisition Corp. II [Member] | Common Stock [Member]
Class Of Stock [Line Items]
Common stock issued to private placement			8,049,555
Common stock issued to private placement, price per share | $ / shares			$ 5.00
Net proceeds of common stock issued to private placement | $			$ 37,200,000