General - Basis of Presentation - Additional Information (Details) $ in Thousands		3 Months Ended				9 Months Ended		12 Months Ended	24 Months Ended
	Apr. 06, 2020 item	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($) item shares	Jun. 30, 2020 USD ($)	Sep. 30, 2019 shares	Sep. 30, 2020 USD ($) item payment shares	Sep. 30, 2019 shares	Dec. 31, 2021	Dec. 31, 2021 USD ($)	Apr. 30, 2020 USD ($)	Apr. 22, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Apr. 17, 2019 USD ($)
Summary of Significant Accounting Policies
Number of parks owned or operated | item			26			26
Valuation allowance			$ 134,700			$ 134,700							$ 130,600
Accrued interest and penalties, income taxes			$ 0			$ 0							0
Number of reporting units | item						1
Antidilutive stock options excluded from computation of diluted shares outstanding (in shares) | shares			5,811,000		3,554,000	5,811,000	3,595,000
Number of contracts in a typical international agreement | item			1			1
Number of upfront payments | payment						1
Number of distinct promises within a typical international agreement | item			3			3
Initial membership term						12 months
Allowance for doubtful accounts			$ 7,700			$ 7,700							$ 8,300
Transformation Initiative
Ride / asset write-offs			9,400			9,400
Total transformation costs			$ 23,051	$ 6,155		29,206
COVID 19 Considerations
Percentage of base salaries reduced for executive officers and full-time salaried employees	25.00%
Percentage of weekly hours reduced for full-time hourly workers	25.00%
Number of weekly hours full-time hourly workers were reduced to | item	30
Amount of deferral of increased investments planned						20,000
Percentage of full time employees salary restored before reopening parks	100.00%
Period prior to reopening of parks in which full salary is restored for full time employees	14 days
Number of parks with suspended operations due to pandemic | item			9
Attendance in current period compared to prior year (as a percent)			35.00%
Other expense (income). net
Transformation Initiative
Consultant costs			$ 12,145	$ 6,155		18,300
Employee termination costs			1,555			1,555
Loss on disposal of assets
Transformation Initiative
Ride / asset write-offs			$ 9,351			$ 9,351
Second Amended and Restated Term Loan B
COVID 19 Considerations
Incremental borrowing capacity										$ 131,000
Maximum borrowing capacity										481,000		$ 350,000		$ 800,000
Interest rate, stated percentage			3.01%			3.01%
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%
Forecast
Transformation Initiative
Ride / asset write-offs									$ 9,000
Total transformation costs		$ 5,000							69,000
Transformation costs paid from cash									$ 60,000
Percentage of investments in 2021 on technology platform								66.67%
Minimum
COVID 19 Considerations
Amount of non-labor costs reduced in current year						$ 30,000
Amount of deferral or elimination of discretional capital projects planned for current year						50,000
Attendance in current period compared to prior year (as a percent)				20.00%
Maximum
COVID 19 Considerations
Amount of non-labor costs reduced in current year						40,000
Amount of deferral or elimination of discretional capital projects planned for current year						$ 60,000
Attendance in current period compared to prior year (as a percent)				25.00%
United States
Summary of Significant Accounting Policies
Number of parks owned or operated | item			23			23
Mexico
Summary of Significant Accounting Policies
Number of parks owned or operated | item			2			2
Canada
Summary of Significant Accounting Policies
Number of parks owned or operated | item			1			1