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) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Significant Accounting Policies [Line Items]      
Trade accounts receivable $ 0   $ 0
Impairment of long-lived assets 0 $ 0  
Fair value movements between Level 2 and Level 3 0 0  
Level 3 [Member]      
Significant Accounting Policies [Line Items]      
Financial instruments classified as Level 3 $ 0 $ 0