Description of the business and summary of significant accounting policies: Property and equipment (Details)	12 Months Ended
	Dec. 31, 2017
Indefeasible rights of use (IRUs) | Minimum
Property and equipment
Depreciation or amortization period	15 years
Indefeasible rights of use (IRUs) | Maximum
Property and equipment
Depreciation or amortization period	20 years
Network equipment | Minimum
Property and equipment
Depreciation or amortization period	3 years
Network equipment | Maximum
Property and equipment
Depreciation or amortization period	8 years
Software
Property and equipment
Depreciation or amortization period	5 years
Building
Property and equipment
Depreciation or amortization period	40 years
Office and other equipment | Minimum
Property and equipment
Depreciation or amortization period	3 years
Office and other equipment | Maximum
Property and equipment
Depreciation or amortization period	7 years
System infrastructure | Minimum
Property and equipment
Depreciation or amortization period	5 years
System infrastructure | Maximum
Property and equipment
Depreciation or amortization period	10 years