v3.19.3.a.u2
Common shares (Details) - USD ($)
$ / shares in Units, $ in Millions
2 Months Ended 12 Months Ended
Dec. 17, 2019
Feb. 26, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Common shares          
Common Stock, No Par Value     $ 0 $ 0  
Common Stock, Shares Authorized, Unlimited     Unlimited Unlimited  
Common Stock, Shares, Issued     108,675,294 108,341,738  
Common Stock, Shares, Outstanding     108,675,294 108,341,738  
Stock Repurchase Program          
Common shares repurchased and canceled     $ 2.5 $ 16.6 $ 0.2
Common shares repurchased and canceled (in shares)     1,064,081 7,772,971  
Normal Course Issuer Bid [Member]          
Stock Repurchase Program          
Public float amount used to determine share amount, percent 10.00%        
Normal Course Issuer Bid [Member] | Subsequent event          
Stock Repurchase Program          
Common shares repurchased and canceled   $ 4.1      
Common shares repurchased and canceled (in shares)   1,742,919      
Normal Course Issuer Bid [Member] | Maximum          
Stock Repurchase Program          
Number of shares authorized for repurchase     10,578,799    
Number of shares that may be purchased per day     9,243