Revenues - Summary of Disaggregation of Broadcast Advertising Revenue by Sales Channel (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation Of Revenue [Line Items]
Total revenue	$ 62,978	$ 68,816	$ 172,343	$ 202,737
Advertising
Disaggregation Of Revenue [Line Items]
Total revenue	37,596	37,345	98,913	109,290
Advertising | Local Direct
Disaggregation Of Revenue [Line Items]
Total revenue	5,464	6,781	15,400	19,292
Advertising | Local Agency
Disaggregation Of Revenue [Line Items]
Total revenue	12,021	14,655	33,460	43,321
Advertising | National Agency
Disaggregation Of Revenue [Line Items]
Total revenue	$ 20,111	$ 15,909	$ 50,053	$ 46,677