v3.19.1
Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Jul. 02, 2018
Dec. 31, 2018
Sep. 30, 2018
 [1]
Jun. 30, 2018
 [1]
Mar. 31, 2018
 [1]
Dec. 31, 2017
Sep. 30, 2017
 [1]
Jun. 30, 2017
 [1]
Mar. 31, 2017
 [1]
Dec. 31, 2018
Dec. 31, 2017
Subsidiary, Sale of Stock [Line Items]                      
Net proceeds from initial public offering                   $ 52,313  
Operating loss   $ (6,925) [1] $ (3,808) $ (1,730) $ (1,328) $ (653) [1] $ (1,135) $ (1,665) $ (1,618) (13,791) $ (5,071)
Accumulated deficit   $ (99,892)       $ (51,319)       $ (99,892) $ (51,319)
Class A Common Stock [Member]                      
Subsidiary, Sale of Stock [Line Items]                      
Shares of common stock issued and sold                   3,125,000  
Initial Public Offering (IPO) [Member] | Class A Common Stock [Member]                      
Subsidiary, Sale of Stock [Line Items]                      
Shares of common stock issued and sold 3,125,000                    
Public offering price, per share $ 18.00                    
Net proceeds from initial public offering $ 48,600                    
Sale of stock sold by stockholders shares 1,562,500                    
[1] The Company's statements of operations were impacted in the third and fourth quarter of 2018 by the recognition of $0.6 million and $1.1 million of stock-based compensation expense, respectively, related to performance-based RSU grants for which achievement of the performance condition became probable.