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Stock based compensation plans (Details) - USD ($)
shares in Millions, $ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Share-based Payment Arrangement [Abstract]      
Share-based compensation arrangement, number of shares available for grant 3.7    
Share-based compensation expense, net of tax $ 12.0 $ 10.8 $ 6.5
Share-based compensation nonvested awards total compensation cost not yet recognized $ 10.9    
Share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition 1 year 7 months 6 days