Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash paid during the period for:
Interest	$ 884	$ 850	$ 636
Income taxes	2,864	2,420	6,555
Non-cash transactions:
Barter revenue	3,570	3,618	3,471
Barter expense	3,677	3,367	3,217
Purchase of treasury shares in connection with exercise of stock options	0	826	0
Acquisition of property and equipment	11	8	49
Use of treasury shares for 401(k) match	$ 252	$ 274	$ 258