Revenue - Summary of Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation Of Revenue [Line Items]
Gross revenue	$ 39,963	$ 38,799	$ 78,414	$ 74,162
Less: Agency commissions and other	5,183	4,618	9,728	8,631
Net revenue	34,780	34,181	68,686	65,531
Local, National and Digital
Disaggregation Of Revenue [Line Items]
Gross revenue	32,243	30,722	60,871	58,619
Network
Disaggregation Of Revenue [Line Items]
Gross revenue	2,954	2,604	5,084	4,084
Special Events
Disaggregation Of Revenue [Line Items]
Gross revenue	1,593	2,043	6,713	5,123
Barter
Disaggregation Of Revenue [Line Items]
Gross revenue	1,360	1,827	2,272	3,323
Other
Disaggregation Of Revenue [Line Items]
Gross revenue	$ 1,813	$ 1,603	$ 3,474	$ 3,013