Commitments and contingencies: Capital leases - fiber lease agreement (Details) - Indefeasible rights of use (IRUs)	12 Months Ended
Dec. 31, 2017
Minimum
Commitments and contingencies
Capital lease term	15 years
Maximum
Commitments and contingencies
Capital lease term	20 years

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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