XML 485 R207.htm IDEA: XBRL DOCUMENT v3.19.1
Related parties - Summary of Remuneration to Related Parties (Parenthetical) (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
N Holland [Member]    
Disclosure of transactions between related parties [line items]    
Salary paid, executive directors and prescribed officers $ 406,700 $ 396,500
P Schmidt [Member]    
Disclosure of transactions between related parties [line items]    
Salary paid, executive directors and prescribed officers 124,150 121,000
B Mattison [Member]    
Disclosure of transactions between related parties [line items]    
Salary paid, executive directors and prescribed officers $ 88,217 $ 86,000