Revenues - Summary of Revenues Disaggregated by Major Source (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation Of Revenue [Line Items]
Total revenue	$ 82,073	$ 74,575	$ 74,329	$ 66,838	$ 73,460	$ 334,555	$ 70,509	$ 57,510	$ 297,815	$ 536,034	$ 258,514
Broadcast Advertising
Disaggregation Of Revenue [Line Items]
Total revenue									169,009	171,715	194,530
Digital Advertising
Disaggregation Of Revenue [Line Items]
Total revenue									80,982	57,098	23,144
Spectrum Usage Rights
Disaggregation Of Revenue [Line Items]
Total revenue									2,976	263,943
Retransmission Consent
Disaggregation Of Revenue [Line Items]
Total revenue									35,066	31,413	29,557
Other
Disaggregation Of Revenue [Line Items]
Total revenue									$ 9,782	$ 11,865	$ 11,283