Revenues - Summary of Disaggregation of Broadcast Advertising Revenue by Sales Channel (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Total revenue	$ 171,683	$ 62,978	$ 45,116	$ 64,249	$ 70,838	$ 68,816	$ 69,241	$ 64,680	$ 344,026	$ 273,575	$ 297,815
Advertising
Disaggregation Of Revenue [Line Items]
Total revenue									152,677	148,082	169,009
Advertising | Local Direct
Disaggregation Of Revenue [Line Items]
Total revenue									21,334	25,972	27,522
Advertising | Local Agency
Disaggregation Of Revenue [Line Items]
Total revenue									48,702	58,425	61,226
Advertising | National Agency
Disaggregation Of Revenue [Line Items]
Total revenue									$ 82,641	$ 63,685	$ 80,261