Nature of Business and Significant Accounting Policies - Barter, Advertising and Marketing Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Barter transactions:
Barter revenue	$ 877	$ 710
Barter expense	(583)	(676)
Barter revenue and expense	294	34
Advertising and Marketing costs:
Advertising and marketing costs	$ 3,000	$ 3,300