Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2017
USD ($)
GeographicalAreas
Segment
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Summary Of Significant Accounting Policies [Line Items]      
Number of operating segment | Segment 1    
Number of geographic segment | GeographicalAreas 1    
Maturity period of highly liquid investments Three months or less    
Realized gains or losses on marketable securities $ 0 $ 0 $ 0
Number of securities in unrealized loss position for more than 12 months 0 0  
Impairment of long-lived assets $ 0    
Provision for unrecognized tax benefits or expense 0    
Grants receivable recognized 1,200,000 $ 0 $ 0
Grants receivable 343,372    
Grants remaining to be awarded $ 2,054,290    
Earliest Tax Year [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Tax position for all open tax years 2008    
Latest Tax Year [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Tax position for all open tax years 2016    
Minimum [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Property and equipment, estimated useful lives 3 years    
Maximum [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Property and equipment, estimated useful lives 5 years    
Level 1 [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Liabilities $ 0    
Level 2 [Member]      
Summary Of Significant Accounting Policies [Line Items]      
Liabilities $ 0