Revenue - Spectrum Segment Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenue	$ 243.8	$ 181.8	$ 415.6	$ 368.4
Total revenue	243.8	181.8	415.6	368.4
Spectrum
Segment Reporting Information [Line Items]
Total revenue	10.6	9.5	21.1	19.6
Network advertising | Spectrum
Segment Reporting Information [Line Items]
Revenue	4.8	4.0	9.5	9.0
Broadcast station | Spectrum
Segment Reporting Information [Line Items]
Revenue	4.5	3.8	8.9	7.3
Network distribution | Spectrum
Segment Reporting Information [Line Items]
Revenue	0.7	1.0	1.6	2.1
Other | Spectrum
Segment Reporting Information [Line Items]
Revenue	$ 0.6	$ 0.7	$ 1.1	$ 1.2