Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation Of Revenue [Line Items]
Total net revenues	$ 6,996	$ 16,334	$ 18,781	$ 24,480
Radio Advertising
Disaggregation Of Revenue [Line Items]
Total net revenues	$ 2,628	$ 7,466	$ 9,008	$ 13,508
Radio Advertising | Revenue, Product and Service Benchmark | Product Concentration Risk
Disaggregation Of Revenue [Line Items]
Percentage of revenue	38.00%	46.00%	48.00%	55.00%
Outdoor Advertising
Disaggregation Of Revenue [Line Items]
Total net revenues	$ 3,030		$ 6,297
Outdoor Advertising | Revenue, Product and Service Benchmark | Product Concentration Risk
Disaggregation Of Revenue [Line Items]
Percentage of revenue	43.00%	0.00%	34.00%	0.00%
Nontraditional
Disaggregation Of Revenue [Line Items]
Total net revenues	$ 80	$ 6,714	$ 248	$ 6,975
Nontraditional | Revenue, Product and Service Benchmark | Product Concentration Risk
Disaggregation Of Revenue [Line Items]
Percentage of revenue	1.00%	41.00%	1.00%	29.00%
Digital
Disaggregation Of Revenue [Line Items]
Total net revenues	$ 340	$ 1,036	$ 1,014	$ 1,750
Digital | Revenue, Product and Service Benchmark | Product Concentration Risk
Disaggregation Of Revenue [Line Items]
Percentage of revenue	5.00%	6.00%	5.00%	7.00%
Other
Disaggregation Of Revenue [Line Items]
Total net revenues	$ 918	$ 1,118	$ 2,214	$ 2,247
Other | Revenue, Product and Service Benchmark | Product Concentration Risk
Disaggregation Of Revenue [Line Items]
Percentage of revenue	13.00%	7.00%	12.00%	9.00%