Summary of significant accounting policies - Non controlling interests (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Non-controlling interests
Distributions to non-controlling interest holders	$ 262	$ 1,003	$ 614
Chicago Concourse Development Group, LLC
Non-controlling interests
Percentage of net profits less capital expenditures of the preceding year allocated to non-controlling interest holders	30.00%
Distributions to non-controlling interest holders	$ 262	1,003	614
Boingo Holding Participacoes Ltda.
Non-controlling interests
Distributions to non-controlling interest holders	$ 0	$ 0	$ 0