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Financial risk management, objectives and policies, Convertible Senior Notes due 2019 and 2021 (Details) - USD ($)
 1 Months Ended 12 Months Ended
Aug. 21, 2020
Dec. 31, 2019
Oct. 31, 2019
Aug. 31, 2018
Sep. 30, 2014
Dec. 31, 2021
Convertible Senior Notes due 2019 [Member]            
Credit Facility [Abstract]            
Aggregate principal amount of convertible senior notes issued       $ 73,000,000.0    
Convertible Senior Notes due 2019 [Member] | Private Placement [Member]            
Credit Facility [Abstract]            
Adjustment to interest rate basis       4.50%    
Convertible Senior Notes due 2019 [Member] | Samco Ltd [Member]            
Credit Facility [Abstract]            
Frequency of periodic repayment           semiannually
Adjustment to interest rate basis         4.50%  
Initial conversion price of common stock (in dollars per share)         $ 8.125  
Initial conversion rate of common stock (in shares)         123.0769  
Aggregate principal amount of convertible senior notes, subjected to anti-dilution         $ 1,000  
Amount converted into shares     $ 26,434,000      
Conversion price (in dollars per share)     $ 6.0216      
Number of shares issued at conversion (in shares)     4,389,858      
Amount of aggregate principal repaid in cash     $ 6,426,000      
Convertible Senior Notes due 2019 [Member] | Samco Ltd [Member] | Private Placement [Member]            
Credit Facility [Abstract]            
Aggregate principal amount of convertible senior notes issued         150,000,000  
Net proceeds from after conversion         $ 145,500,000  
Convertible Senior Notes due 2021 [Member]            
Credit Facility [Abstract]            
Aggregate principal amount of convertible senior notes issued       $ 80,300,000    
Adjustment to interest rate basis       4.50%    
Initial conversion price of common stock (in dollars per share) $ 5.3470          
Initial conversion rate of common stock (in shares) 187.0208 167        
Aggregate principal amount of convertible senior notes, subjected to anti-dilution $ 1,000 $ 1,000        
Aggregate number of shares of common stock to be issued at conversion (in shares) 23,377,397          
Percentage of principal amount plus accrued and unpaid interest to be redeemed           100.00%
Convertible Senior Notes due 2021 [Member] | Private Placement [Member]            
Credit Facility [Abstract]            
Aggregate principal amount of convertible senior notes issued   $ 124,999,000   $ 125,000,000.0    
Net proceeds from after conversion       $ 38,900,000    
Frequency of periodic repayment           semiannually
Adjustment to interest rate basis       4.50%    
Initial conversion price of common stock (in dollars per share)       $ 6.2599    
Initial conversion rate of common stock (in shares)       159.7470    
Principal amount of convertible senior notes issued amount       $ 44,700,000    
Aggregate principal amount of convertible senior notes, subjected to anti-dilution       1,000    
Net proceeds from conversion of senior notes       $ 41,600,000