Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.19.1
Summary of Significant Accounting Policies - Additional Information (Detail)
3 Months Ended
Mar. 31, 2019
USD ($)
Segment
Mar. 31, 2018
USD ($)
Jan. 01, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2016
PerformanceObligation
Summary Of Significant Accounting Policies [Line Items]          
Realized gains and losses on investments $ 0 $ 0      
Other-than-temporary declines in value of marketable securities 0        
Impairment losses not recognized $ 0        
Unrecognized tax benefits that would, if recognized, affect the Company’s effective tax rate       $ 0  
Number of operating segment | Segment 1        
ROU assets $ 514,000   $ 600,000    
Lease liabilities 627,000   $ 700,000    
Collaboration Agreement [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Unrecognized royalty revenue $ 0        
Collaboration Agreement [Member] | Novartis [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Number of significant performance obligations | PerformanceObligation         2
Minimum [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Estimated useful lives of the assets 3 years        
Maximum [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Estimated useful lives of the assets 5 years