Revenue - Spectrum Segment Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenue	$ 394.8	$ 170.5	$ 810.4	$ 538.9
Spectrum
Segment Reporting Information [Line Items]
Revenue	10.2	9.7	31.3	29.3
Broadcast station | Spectrum
Segment Reporting Information [Line Items]
Revenue	4.7	4.0	13.6	11.3
Network advertising | Spectrum
Segment Reporting Information [Line Items]
Revenue	4.2	4.1	13.7	13.1
Network distribution | Spectrum
Segment Reporting Information [Line Items]
Revenue	0.8	1.0	2.5	3.0
Other | Spectrum
Segment Reporting Information [Line Items]
Revenue	$ 0.5	$ 0.6	$ 1.5	$ 1.9