Spectrum repacking reimbursements and other, net - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unusual or Infrequent Item, or Both [Line Items]
Reimbursement from spectrum repacking		$ 13,180,000	$ 16,974,000	$ 7,400,000
Gain on sale of real estate			2,900,000	6,000,000.0
Asset impairment charges			9,100,000
Impairment of indefinite-lived intangible assets		0	$ 0	0
FCC licenses
Unusual or Infrequent Item, or Both [Line Items]
Impairment of indefinite-lived intangible assets		$ 1,100,000
Trade Names
Unusual or Infrequent Item, or Both [Line Items]
Impairment of indefinite-lived intangible assets	$ 2,100,000
Hurricane Harvey
Unusual or Infrequent Item, or Both [Line Items]
Net expense impact from hurricane				$ 1,100,000