Revenues - Summary of Disaggregation of Broadcast Advertising Revenue by Sales Channel (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Total revenue	$ 148,880	$ 64,249
Advertising
Disaggregation Of Revenue [Line Items]
Total revenue	33,675	38,728
Advertising | Local Direct
Disaggregation Of Revenue [Line Items]
Total revenue	5,240	5,843
Advertising | Local Agency
Disaggregation Of Revenue [Line Items]
Total revenue	13,188	13,566
Advertising | National Agency
Disaggregation Of Revenue [Line Items]
Total revenue	$ 15,247	$ 19,319