Revenues - Summary of Disaggregation of Broadcast Advertising Revenue by Sales Channel (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disaggregation Of Revenue [Line Items]
Total revenue	$ 37,709	$ 42,788
Local Direct
Disaggregation Of Revenue [Line Items]
Total revenue	14,593	16,503
Local Agency
Disaggregation Of Revenue [Line Items]
Total revenue	6,916	7,403
National Agency
Disaggregation Of Revenue [Line Items]
Total revenue	$ 16,200	$ 18,882