Revenue - Summary of Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation Of Revenue [Line Items]
Gross revenue	$ 39,287	$ 37,334	$ 117,701	$ 111,496
Less: Agency commissions and other	5,249	4,543	14,977	13,174
Net revenue	34,038	32,791	102,724	98,322
Local, National and Digital
Disaggregation Of Revenue [Line Items]
Gross revenue	32,976	30,460	93,847	89,079
Network
Disaggregation Of Revenue [Line Items]
Gross revenue	2,894	2,507	7,978	6,591
Special Events
Disaggregation Of Revenue [Line Items]
Gross revenue	53	1,062	6,766	6,185
Barter
Disaggregation Of Revenue [Line Items]
Gross revenue	1,770	1,709	4,042	5,032
Other
Disaggregation Of Revenue [Line Items]
Gross revenue	$ 1,594	$ 1,596	$ 5,068	$ 4,609