v3.10.0.1
Summary of Significant Accounting Policies - Additional Information (Detail)
9 Months Ended
Sep. 30, 2018
USD ($)
Segment
Institution
Dec. 31, 2017
USD ($)
Institution
Summary Of Significant Accounting Policies [Line Items]    
Number of operating segment | Segment 1  
Significant uncertain tax positions | $ $ 0 $ 0
Number of principal financial institutions in cash deposit | Institution 2 2
Minimum [Member]    
Summary Of Significant Accounting Policies [Line Items]    
Furniture and equipment estimated useful lives 3 years  
Maximum [Member]    
Summary Of Significant Accounting Policies [Line Items]    
Furniture and equipment estimated useful lives 7 years