Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash paid during the period for:
Interest	$ 850	$ 636	$ 718
Income taxes	2,420	6,555	4,192
Non-cash transactions:
Barter revenue	3,618	3,471	3,433
Barter expense	3,367	3,217	3,270
Purchase of treasury shares in connection with exercise of stock options	826	0	3,294
Acquisition of property and equipment	8	49	44
Acquisition of broadcast properties	0	0	50
Use of treasury shares for 401(k) match	$ 274	$ 258	$ 244