v3.19.2
Nature of Organization and Operations - Additional Information (Detail)
 3 Months Ended
Mar. 15, 2017
USD ($)
$ / shares
shares
Jun. 30, 2018
USD ($)
shares
Jun. 30, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
Mar. 14, 2017
shares
Mar. 09, 2017
$ / shares
shares
Class Of Stock [Line Items]              
Common stock, shares authorized     300,000,000 300,000,000     100,000,000
Common stock, par value | $ / shares     $ 0.0001 $ 0.0001     $ 0.0001
Preferred stock, shares authorized     10,000,000 10,000,000     10,000,000
Preferred stock, par value | $ / shares     $ 0.0001 $ 0.0001     $ 0.0001
Capital stock conversion basis ratio 2.3336572            
Common stock, shares outstanding     40,588,004 40,588,004      
Warrants issued to purchase common stock, exercise price | $ / shares     $ 5.00 $ 5.00      
Cash and cash equivalents | $   $ 68,783,210 $ 48,157,010 $ 62,614,010 $ 20,264,109    
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 sold in offering   11,688,000          
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]              
Net proceeds from issuance of common stock in private placement | $ $ 37,200,000            
Zeta Acquisition Corp. II [Member] | Common Stock [Member] | Private Placement [Member]              
Class Of Stock [Line Items]              
Common stock sold in offering 8,049,555            
Common stock issued to private placement, price per share | $ / shares $ 5.00