Stock incentive plans - Compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Recognized stock-based compensation expense
Total stock-based compensation expense	$ 1,537	$ 2,344
Stock-based compensation expense capitalized	149	230
Out-of-period adjustments	481
Network operations
Recognized stock-based compensation expense
Total stock-based compensation expense	348	506
Development and technology
Recognized stock-based compensation expense
Total stock-based compensation expense	158	303
Selling and marketing
Recognized stock-based compensation expense
Total stock-based compensation expense	422	529
General and administrative
Recognized stock-based compensation expense
Total stock-based compensation expense	$ 609	$ 1,006