v3.19.3.a.u2
Financial Risk Management and Financial Instruments - Summary of PWERM Valuations (Details)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Market Approach Under PWERM | Low Case Public Company    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings   35.00%
Market Approach Under PWERM | Bottom of Range | High Case Public Company    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 55.00% 25.00%
Market Approach Under PWERM | Bottom of Range | Low Case Public Company    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 28.00%  
Market Approach Under PWERM | Bottom of Range | High Case Transaction    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 0.00% 4.00%
Market Approach Under PWERM | Bottom of Range | Low Case Transaction    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 0.00% 4.00%
Market Approach Under PWERM | Top of Range | High Case Public Company    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 70.00% 40.00%
Market Approach Under PWERM | Top of Range | Low Case Public Company    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 35.00%  
Market Approach Under PWERM | Top of Range | High Case Transaction    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 3.00% 6.00%
Market Approach Under PWERM | Top of Range | Low Case Transaction    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 2.00% 6.00%
Income and Market Approaches Under PWERM | Bottom of Range    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 2.00% 5.00%
Income and Market Approaches Under PWERM | Top of Range    
Disclosure Of Financial Risk Management And Financial Instruments [Line Items]    
Percentage of weightings 5.00% 30.00%