Revenues - Summary of Disaggregation of Broadcast Advertising Revenue by Sales Channel (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation Of Revenue [Line Items]
Total revenue	$ 199,008	$ 62,978	$ 526,298	$ 172,343
Advertising
Disaggregation Of Revenue [Line Items]
Total revenue	40,495	37,596	110,608	98,913
Advertising | Local Direct
Disaggregation Of Revenue [Line Items]
Total revenue	5,881	5,464	16,850	15,400
Advertising | Local Agency
Disaggregation Of Revenue [Line Items]
Total revenue	16,122	12,021	44,529	33,460
Advertising | National Agency
Disaggregation Of Revenue [Line Items]
Total revenue	$ 18,492	$ 20,111	$ 49,229	$ 50,053