Description of Business (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) item payment	Apr. 30, 2020 USD ($)	Apr. 22, 2020 USD ($)	Mar. 31, 2020 USD ($)	Apr. 17, 2019 USD ($)
Summary of Significant Accounting Policies
Number of parks owned or operated	26
Period of operation of theme parks by the former SFEC under Six Flags name (in years)	40 years
Number of parks branded as "Six Flags" parks	22
Number of reporting units	1
Number of upfront payments | payment	1
Initial membership term	12 months
COVID 19 Considerations
Percentage of base salaries reduced for full-time salaried employees	25.00%
Number of parks with suspended operations due to pandemic	20
Transformation Initiative
Total transformation costs | $	$ 34,576
Number of revenue initiatives	5
Number of cost initiatives	3
Number of satellite offices closed	2
Other expense (income). net
Transformation Initiative
Consultant costs | $	$ 20,460
Employee termination costs | $	4,362
Loss on disposal of assets
Transformation Initiative
Ride / asset write-offs | $	$ 9,754
Second Amended and Restated Term Loan B
COVID 19 Considerations
Incremental borrowing capacity | $		$ 131,000
Maximum borrowing capacity | $		481,000		$ 350,000	$ 800,000
Senior Unsecured 2025 Notes
COVID 19 Considerations
Debt instrument, face amount | $		$ 725,000
Interest rate, stated percentage		7.00%
Senior Unsecured 2025 Notes | Six Flags Theme Parks Inc.
COVID 19 Considerations
Debt instrument, face amount | $			$ 725,000
Interest rate, stated percentage			7.00%
United States
Summary of Significant Accounting Policies
Number of parks owned or operated	23
Mexico
Summary of Significant Accounting Policies
Number of parks owned or operated	2
Canada
Summary of Significant Accounting Policies
Number of parks owned or operated	1