Summary of Significant Accounting Policies - Revenue (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) item	Jun. 30, 2018 USD ($)
Revenue recognition
Revenues from barter transaction	$ 261,000	$ 239,000	$ 261,000	$ 239,000
Contract with customer liability rollforward
Balance, beginning of period	4,496,000	5,298,000	1,140,000	1,249,000
Reductions from beginning balance	3,345,000	4,000,000	739,000	778,000
Additional liabilities recorded during the period	1,841,000	1,648,000	5,197,000	5,697,000
Reduction of additional liabilities recorded during the period, not from beginning balance	984,000	1,246,000	3,590,000	4,468,000
Balance, end of period	2,008,000	$ 1,700,000	2,008,000	$ 1,700,000
Unsatisfied performance obligations amount	$ 3,272,000		$ 3,272,000
Remittance period (in days)			30 days
Gross broadcast rights fees retained by NASCAR (in percent)	10.00%		10.00%
Gross broadcast rights fees recorded as revenue (in percent)	90.00%		90.00%
Gross broadcast rights fees payable to the event (in percent)	25.00%		25.00%
Minimum
Contract with customer liability rollforward
Contract term (in years)			1 year
Maximum
Contract with customer liability rollforward
Contract term (in years)			3 years
NASCAR
Revenue recognition
Events excluded from revenue based on contract with customers (number) | item			2
Firefly Music Festival ("Firefly")
Revenue recognition
Events excluded from revenue based on contract with customers (number)			1
Events 2019
Revenue recognition
Contract liabilities	$ 1,997,000		$ 1,997,000
Events 2020
Revenue recognition
Contract liabilities	$ 11,000		$ 11,000