Summary of significant accounting policies - Narrative (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) carrier	Dec. 31, 2018 USD ($)
Concentration Risk [Line Items]
Restricted cash	$ 923	$ 376
Carriers company wrote with \| carrier	100
Carriers company wrote with, provide national coverage \| carrier	35
Interest related to franchise fee	$ 606	418
Weighted average amortization period (years)	3 years 1 month 17 days
Unearned revenue/ contract liabilities	$ 2,771
Advertising expense	812	$ 521
Future minimum payments	$ 22,300
Carrier One \| Total revenue \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	16.00%	17.00%
Carrier Two \| Total revenue \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk percentage	10.00%	11.00%
Web domain
Concentration Risk [Line Items]
Weighted average amortization period (years)	15 years
Software costs
Concentration Risk [Line Items]
Weighted average amortization period (years)	3 years
Initial Franchise Fee
Concentration Risk [Line Items]
Unearned revenue/ contract liabilities	$ 0	$ 530
Furniture, fixtures, and equipment
Concentration Risk [Line Items]
Property, plant and equipment, useful life	5 years
Computer equipment
Concentration Risk [Line Items]
Property, plant and equipment, useful life	3 years

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