Revenues - Summary of Revenues Disaggregated by Major Source (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Total revenue	$ 74,575	$ 334,555	$ 215,742	$ 462,574
Broadcast Advertising
Disaggregation Of Revenue [Line Items]
Total revenue	40,183	42,104	119,425	128,918
Digital Advertising
Disaggregation Of Revenue [Line Items]
Total revenue	22,431	17,131	61,233	36,794
Spectrum Usage Rights
Disaggregation Of Revenue [Line Items]
Total revenue	1,178	263,943	1,809	263,943
Retransmission Consent
Disaggregation Of Revenue [Line Items]
Total revenue	8,432	8,494	26,428	23,925
Other
Disaggregation Of Revenue [Line Items]
Total revenue	$ 2,351	$ 2,883	$ 6,847	$ 8,994