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Description of the business and recent developments: Revenue recognition (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Recent accounting pronouncements- adopted      
Maximum contract lengths for billing due upon receipts (in months) 60 months    
Contract costs $ 21.4 $ 20.6  
ASU 2014-09      
Recent accounting pronouncements- adopted      
Service revenue recognized 4.6 4.4 $ 4.4
Amortization expense for contract costs $ 18.4 $ 17.1 $ 17.3