Summary of Significant Accounting Policies - Revenue recognition (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) item	Sep. 30, 2019 USD ($)
Revenue recognition
Refund issued to patrons			$ 1,383,000
Percentage of bonus value on tickets to next year's event			20.00%
Revenues from barter transaction			$ 213,000	$ 261,000
Contract with customer liability rollforward
Balance, beginning of period	$ 3,676,000	$ 2,008,000	976,000	1,140,000
Reductions from beginning balance	(2,342,000)		(271,000)	(739,000)
Additional liabilities recorded during the period	619,000	2,518,000	3,623,000	7,715,000
Reduction of additional liabilities recorded during the period, not from beginning balance	(528,000)		(2,903,000)	(3,590,000)
Balance, end of period	1,425,000	$ 4,526,000	1,425,000	$ 4,526,000
Unsatisfied performance obligations amount	$ 3,115,000		$ 3,115,000
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
Events 2021
Revenue recognition
Contract liabilities	$ 1,345,000		$ 1,345,000
Events 2022 [Member]
Revenue recognition
Contract liabilities	$ 80,000		$ 80,000