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Commitments and Contingencies (Details)				1 Months Ended			6 Months Ended		12 Months Ended
Commitments and Contingencies (Details)	Apr. 08, 2020 item	Jan. 07, 2016 USD ($)	Apr. 01, 1998 USD ($)	May 31, 2020 USD ($) shares	Apr. 30, 2020 item	May 31, 2019 shares	Jun. 30, 2020 USD ($) multiple	Jun. 30, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2017 claim	Apr. 07, 2017 item
Details of commitments and contingencies
Acquisition of capital stock of the former Six Flags Entertainment Corporation, paid in cash			$ 976,000,000.0
Redemption value of noncontrolling interests							$ 524,300,000
Additions to property and equipment							75,623,000	$ 96,762,000
Total loans receivable from the partnerships that own partnership parks							239,300,000			$ 239,300,000
Number of questions certified for consideration by appellate court \| item												2
Number of claims filed					2						4
Number of claims consolidated \| item	3
Minimum
Details of commitments and contingencies
Range of possible loss per aggrieved party							100
Maximum
Details of commitments and contingencies
Range of possible loss per aggrieved party							1,000
BIPA \| Minimum
Details of commitments and contingencies
Range of possible loss per aggrieved party		$ 1,000
BIPA \| Maximum
Details of commitments and contingencies
Range of possible loss per aggrieved party		$ 5,000
Multi-layered general liability policies
Details of commitments and contingencies
Excess liability coverage per occurrence							100,000,000.0
Self-insured retention per occurrence							2,000,000.0
Deductible per occurrence applicable to all claims in the policy year							500,000
Workers' compensation claims
Details of commitments and contingencies
Deductible per occurrence applicable to all claims in the policy year							750,000
Workers' compensation claims \| November 16, 2001 - November 15, 2003
Details of commitments and contingencies
Deductible per occurrence applicable to all claims in the policy year							500,000
Information security and privacy liability insurance policy
Details of commitments and contingencies
Self-insured retention per occurrence							250,000
Insurance value maintained							10,000,000.0
Amended And Restated Term Loan B As Amended June 2017
Details of commitments and contingencies
Additional contingent borrowing capacity							$ 350,000,000.0
Six Flags over Georgia
Details of commitments and contingencies
Limited partner interests owned (as a percent)							31.40%
Remaining redeemable units (as a percent)							68.60%
Six Flags over Texas
Details of commitments and contingencies
Purchase price of partnership units				$ 3,400,000
Limited partner interests owned (as a percent)							53.90%
Units purchased in partnership parks (in units) \| shares						1.5675
Remaining redeemable units (as a percent)							46.10%
Six Flags over Texas and Georgia
Details of commitments and contingencies
Rolling period for making minimum capital expenditure at each of the Partnership Parks							5 years
Percentage of capital expenditures to Partnership Parks' revenues							6.00%
Weighted average period of the park's EBITDA for calculation of value of purchase price							4 years
Additions to property and equipment										21,100,000
Cash generated from operating activities by partnerships, after deduction of capital expenditures and excluding the impact of short-term intercompany advances										$ 79,900,000
Six Flags over Georgia
Details of commitments and contingencies
Purchase price of partnership units				$ 1,500,000
Specified multiple for purchase price valuation (in multipliers) \| multiple							8.0
Specified price for purchase of partnership parks							$ 409,700,000
Redemption value of noncontrolling interests							$ 281,000,000.0
Six Flags over Georgia \| Six Flags over Georgia
Details of commitments and contingencies
Units purchased in partnership parks (in units) \| shares				0.375
Six Flags over Texas
Details of commitments and contingencies
Specified multiple for purchase price valuation (in multipliers) \| multiple							8.5
Specified price for purchase of partnership parks							$ 527,400,000
Redemption value of noncontrolling interests							$ 243,300,000
Scenario, Forecast \| Six Flags over Texas and Georgia
Details of commitments and contingencies
Annual distributions by general partners to limited partners in partnership parks									$ 74,200,000
Share of Partnership Parks' annual distributions paid to Six Flags Entertainment Corporation									32,900,000
Additions to property and equipment									$ 16,000,000.0