Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.8.0.1
Summary of Significant Accounting Policies - Additional Information (Detail)
9 Months Ended
Sep. 30, 2017
USD ($)
Segment
Sep. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Property, Plant and Equipment [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    
Minimum [Member]      
Property, Plant and Equipment [Line Items]      
Estimated useful lives of the assets 3 years    
Maximum [Member]      
Property, Plant and Equipment [Line Items]      
Estimated useful lives of the assets 5 years