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) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Significant Accounting Policies [Line Items]      
Trade accounts receivable $ 0 $ 110,000  
Impairment of long-lived assets 0 0 $ 0
Fair value movements between Level 2 and Level 3 0 0 0
Research and development expense 11,556,000 5,638,000 2,766,000
Income tax expense (benefit) 0 0 0
Accounting Standards Update 2016-09 [Member]      
Significant Accounting Policies [Line Items]      
Income tax expense (benefit) (813,000)    
Net impact of adoption 0    
Level 3 [Member]      
Significant Accounting Policies [Line Items]      
Financial instruments classified as Level 3 0 0 0
Related-party In-licensing [Member]      
Significant Accounting Policies [Line Items]      
Research and development expense 93,000 44,000 86,000
Third-party In-licensing [Member]      
Significant Accounting Policies [Line Items]      
Research and development expense $ 447,000 $ 539,000 $ 165,000