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Description of the business and summary of significant accounting policies: Revenue recognition (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Dec. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Recent accounting pronouncements- adopted      
Maximum contract lengths for billing due upon receipts (in months)   60 months  
Capitalized Contract Cost, Net $ 18.7 $ 18.7 $ 18.5
ASU 2014-09      
Recent accounting pronouncements- adopted      
Service revenue recognized 4.4 5.0  
Amortization expense for contract costs $ 17.3 $ 16.8