Accounting Policies - Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total revenues	$ 536,932	$ 524,080	$ 1,053,685	$ 1,026,170
Advertising & Marketing Services
Disaggregation of Revenue [Line Items]
Total revenues	289,569	281,847	553,971	564,786
Subscription
Disaggregation of Revenue [Line Items]
Total revenues	236,162	209,363	477,737	414,919
Political
Disaggregation of Revenue [Line Items]
Total revenues	3,229	25,709	5,933	33,315
Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 7,972	$ 7,161	$ 16,044	$ 13,150