Summary of significant accounting policies - Non controlling interests (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Non-controlling interests
Distributions to non-controlling interest holders	$ 614	$ 125	$ 286
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	$ 614	125	286
Boingo Holding Participacoes Ltda.
Non-controlling interests
Distributions to non-controlling interest holders	$ 0	$ 0	$ 0