Goodwill and other intangible assets - Intangible Assets and Goodwill (Details) $ in Thousands	3 Months Ended
	Jun. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($) station
Goodwill and Intangible Assets Disclosure [Line Items]
Goodwill, gross		$ 2,968,693	$ 2,950,587
Total indefinite-live and amortizable intangible assets		2,719,495	2,730,066
Goodwill, accumulated amortization		0	0
Amortizable intangible assets, accumulated amortization		(218,468)	$ (168,452)
Number of stations acquired | station			15
Retransmission agreements
Goodwill and Intangible Assets Disclosure [Line Items]
Amortizable intangible assets, gross		235,215	$ 256,533
Amortizable intangible assets, accumulated amortization		(130,236)	(105,212)
Network affiliation agreements
Goodwill and Intangible Assets Disclosure [Line Items]
Amortizable intangible assets, gross		309,503	309,496
Amortizable intangible assets, accumulated amortization		(66,569)	(48,174)
Other
Goodwill and Intangible Assets Disclosure [Line Items]
Amortizable intangible assets, gross		70,610	73,305
Amortizable intangible assets, accumulated amortization		(21,663)	(15,066)
Television and radio station FCC broadcast licenses
Goodwill and Intangible Assets Disclosure [Line Items]
Indefinite-lived intangibles, gross		$ 2,104,167	$ 2,090,732
Brand name
Goodwill and Intangible Assets Disclosure [Line Items]
Impairment of brand name	$ 2,100