Goodwill and Other Intangible Assets - Composition of Company's Acquired Intangible Assets and Associated Accumulated Amortization (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Intangible Assets [Line Items]
Gross Carrying Amount	$ 114,390	$ 94,890
Accumulated Amortization	87,632	81,770
Net Carrying Amount	26,758	13,120
Intangible assets not subject to amortization:
Total intangible assets	277,921	233,821
FCC Licenses and Spectrum Usage Rights
Intangible assets not subject to amortization:
Licenses	$ 251,163	220,701
Television network affiliation agreements
Schedule Of Intangible Assets [Line Items]
Weighted average remaining life in years	9 years
Gross Carrying Amount	$ 67,489	65,089
Accumulated Amortization	55,560	53,492
Net Carrying Amount	$ 11,929	11,597
Customer base
Schedule Of Intangible Assets [Line Items]
Weighted average remaining life in years	5 years
Gross Carrying Amount	$ 9,146	3,146
Accumulated Amortization	3,839	2,664
Net Carrying Amount	$ 5,307	482
Pre-sold advertising contracts and other
Schedule Of Intangible Assets [Line Items]
Weighted average remaining life in years	6 years
Gross Carrying Amount	$ 37,755	26,655
Accumulated Amortization	28,233	25,614
Net Carrying Amount	$ 9,522	$ 1,041