Quarterly report pursuant to Section 13 or 15(d)

Debt (Exchangeable Senior Debentures) (Details)

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Debt (Exchangeable Senior Debentures) (Details) - Exchangeable senior debentures - 1.75% Exchangeable Debentures
9 Months Ended
Jun. 18, 2018
USD ($)
$ / shares
shares
Sep. 30, 2020
Debt Instrument [Line Items]    
Interest rate 1.75%  
Threshold percentage of conversion price to stock price trigger   130.00%
Number of consecutive trading days in measurement period   20 days
Number of business days in measurement period   30 days
Exchangeable debentures term   1 year
Charter    
Debt Instrument [Line Items]    
Exchangeable ratio 2.6989  
Exchangeable price (in dollars per share) | $ / shares $ 370.52  
Number of shares exchangeable (in shares) | shares 1,288,051  
Redemption price (as a percent) 100.00%  
Debt instrument, face amount per debenture | $ $ 1,000