Description of business, basis of presentation and summary of significant accounting policies - Narrative (Detail)		12 Months Ended
		Dec. 31, 2020 USD ($) station market segment	Dec. 31, 2019 USD ($) investment	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) investment
Significant Accounting Policies [Line Items]
Number of television stations | station		64
Number of radio stations | station		2
Number of markets In which entity operates | market		51
Number of operating segments | segment		1
Number of reportable segments | segment		1
Write-offs of accounts receivable		$ 4,700,000	$ 3,000,000.0	$ 3,900,000
Goodwill		2,968,693,000	2,950,587,000	2,596,863,000
Impairment of indefinite-lived intangible assets		0	0	0
Gain on sale of equity investments			$ 19,700,000
Number of investments | investment			4
Investments in non-public businesses, non-operating expense		20,300,000	$ 32,400,000
Impairment charge to cost method investments		9,200,000		2,000,000.0
Gain on other equity investment			5,900,000
Impairment charge on debt investments				2,000,000.0
Programming expense		71,100,000	60,800,000	53,400,000
Syndicated programming rights		47,331,000	49,616,000
Cumulative prior period effect		$ (2,058,095,000)	(1,590,377,000)	(1,340,924,000)	$ (995,041,000)
Submission period for customers to submit payments		Our customers submit payments monthly, generally within 60-90 days after the month that the service was provided.
Cost of revenues	[1]	$ 1,503,287,000	1,228,237,000	1,065,933,000
Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Cumulative prior period effect					$ 3,724,000
FCC licenses
Significant Accounting Policies [Line Items]
Intangible assets acquired		897,700,000
Impairment of indefinite-lived intangible assets		1,100,000
Other FCC licenses		$ 1,230,000,000
Restricted Stock
Significant Accounting Policies [Line Items]
Requisite service period		4 years
Performance Shares
Significant Accounting Policies [Line Items]
Requisite service period		3 years
Cost of Sales
Significant Accounting Policies [Line Items]
Bad debt expense		$ 8,000,000.0	2,400,000	3,900,000
Minimum | Building and Improvements
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life (in years)		10 years
Minimum | Machinery, Equipment, and Fixtures
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life (in years)		3 years
Maximum | Building and Improvements
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life (in years)		40 years
Maximum | Machinery, Equipment, and Fixtures
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life (in years)		25 years
Advertising | Selling, General and Administrative Expenses
Significant Accounting Policies [Line Items]
Cost of revenues		$ 5,800,000	$ 9,400,000	$ 10,400,000
Debt Investments
Significant Accounting Policies [Line Items]
Number of investments | investment					1
Impairment charge to cost method investments					$ 5,800,000

[1] Cost of revenues exclude charges for depreciation and amortization expense, which are shown separately above.