Accounting policies - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenues	$ 732,908	$ 577,627	$ 1,459,959	$ 1,261,816
Subscription
Disaggregation of Revenue [Line Items]
Total revenues	375,081	323,475	761,818	656,277
Advertising & Marketing Services
Disaggregation of Revenue [Line Items]
Total revenues	340,889	229,083	663,723	524,236
Political
Disaggregation of Revenue [Line Items]
Total revenues	9,581	17,544	19,009	64,931
Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 7,357	$ 7,525	$ 15,409	$ 16,372