Property and equipment: Installment payment agreement (Details) - Network equipment - Note obligations $ in Millions	1 Months Ended
Mar. 31, 2016 payment installment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Installment payment agreement
Term of debt (in months)	24 months
Number of payments first six months \| payment	0
Number of equal payments \| installment	18
Outstanding obligation		$ 10.7	$ 5.5
Unamortized discount		$ 0.4	$ 0.3

Amount, after accumulated amortization, of debt discount.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28541-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Name:	us-gaap_DebtInstrumentUnamortizedDiscount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant