Accounting policies - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Total revenues	$ 774,123	$ 727,051
Subscription
Disaggregation of Revenue [Line Items]
Total revenues	391,654	386,737
Advertising & Marketing Services
Disaggregation of Revenue [Line Items]
Total revenues	354,467	322,834
Political
Disaggregation of Revenue [Line Items]
Total revenues	17,965	9,428
Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 10,037	$ 8,052