Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.10.0.1
Summary of Significant Accounting Policies - Additional Information (Detail)
6 Months Ended
Jun. 30, 2018
USD ($)
Segment
Jun. 30, 2017
USD ($)
Jan. 01, 2018
USD ($)
Dec. 31, 2017
USD ($)
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        
Accumulated deficit $ (178,133,000)     $ (168,007,000)  
ASU No. 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Accumulated deficit     $ 600,000    
Collaboration Agreement [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Unrecognized royalty revenue 0        
Collaboration Agreement [Member] | ASU No. 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Revenue recognized 1,400,000        
Collaboration Agreement [Member] | ASU No. 2014-09 [Member] | Calculated under Revenue Guidance in Effect before Topic 606 [Member]          
Summary Of Significant Accounting Policies [Line Items]          
Revenue recognized $ 17,100,000        
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