Amount of annual interest cost saving from a borrowing rate reduction, excluding the cost to execute the transaction.

No definition available.

Name:	six_AnnualInterestCostSavingsFromBorrowingRateReductionExcludingTransactionExecutionCost
Namespace Prefix:	six_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Interest rate reduction resulting from the amendment of long-term debt.

+ References

No definition available.

+ Details

Name:	six_DebtAmendmentBasisSpreadIncreaseDecrease
Namespace Prefix:	six_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of the required payments applied to interest for the first payment period.

+ References

No definition available.

+ Details

Name:	six_DebtInstrumentPeriodicPaymentInterestFirstPayment
Namespace Prefix:	six_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Incremental borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

No definition available.

+ Details

Name:	six_LineOfCreditFacilityIncrementalBorrowingCapacity
Namespace Prefix:	six_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash outflow during the period from the pre- payment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

+ References

No definition available.

+ Details

Name:	six_PrePaymentOfDebt
Namespace Prefix:	six_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the proceeds from issuance of debt instruments that are utilized for extinguishment of existing debt instruments.

+ References

No definition available.

+ Details

Name:	six_ProceedsFromIssuanceOfDebtUtilizedForExtinguishmentOfExistingDebtInstruments
Namespace Prefix:	six_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the required periodic payments applied to interest.

+ References

+ Details

Name:	us-gaap_DebtInstrumentPeriodicPaymentInterest
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

+ Details

Name:	us-gaap_DerivativeNumberOfInstrumentsHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Gross amount of debt extinguished.

+ References

No definition available.

+ Details

Name:	us-gaap_ExtinguishmentOfDebtAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12355-112629

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 50
-Section 40
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12317-112629

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainsLossesOnExtinguishmentOfDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

+ Details

Name:	us-gaap_PaymentsOfDebtIssuanceCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=six_InterestRateSwapSecondMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_AmendedAndRestatedRevolvingLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_AmendedAndRestatedTermLoanBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_CreditFacility2015Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_CreditFacility2015TermLoanBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_AmendedAndRestatedTermLoanBAsAmendedJune2017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_SecondAmendedAndRestatedCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_SecondAmendedAndRestatedRevolvingLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_SecondAmendedAndRestatedTermLoanBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_SeniorUnsecured2024NotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_SeniorUnsecured2024NotesAddonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_SeniorUnsecured2025NotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=six_SeniorUnsecured2027NotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term Indebtedness - Additional Information (Details)								1 Months Ended	12 Months Ended
	Apr. 22, 2020 USD ($)	Oct. 18, 2019 USD ($)	Oct. 17, 2019	Apr. 17, 2019 USD ($)	Apr. 13, 2017 USD ($)	Jan. 31, 2017 USD ($)	Jun. 16, 2016 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Apr. 30, 2020 USD ($)	Apr. 08, 2020 USD ($)	Apr. 07, 2020 USD ($)	Aug. 31, 2019 USD ($) item	Jun. 30, 2019 USD ($) item	Apr. 16, 2019 USD ($)
Summary of Long-term debt
Payments of debt issuance costs									$ 24,987,000	$ 9,911,000	$ 793,000
Loss on debt extinguishment, net									6,106,000	6,484,000	$ 0
Long-term debt									2,653,490,000
Proceeds from issuance of debt utilized for extinguishment of existing debt instruments							$ 150,000,000.0
Interest Rate Swap
Summary of Long-term debt
Notional amount																$ 300,000,000.0
Interest Rate Swap Second Agreements
Summary of Long-term debt
Notional amount															$ 400,000,000.0
LIBOR
Summary of Long-term debt
Basis spread on variable rate			2.00%
Amended And Restated Revolving Loan
Summary of Long-term debt
Maximum borrowing capacity									481,000,000.0
Letters of credit outstanding, amount									$ 21,000,000.0	20,800,000
Commitment fee percentage									0.30%
Amended And Restated Term Loan B
Summary of Long-term debt
Maximum borrowing capacity									$ 479,000,000.0
Loss on debt extinguishment, net	$ 5,100,000
Repayment of debt	315,000,000.0
2015 Revolving Loan
Summary of Long-term debt
Maximum borrowing capacity																	$ 250,000,000.0
Credit Facility 2015 - Term Loan B
Summary of Long-term debt
Maximum borrowing capacity																	$ 700,000,000.0
Amended And Restated Term Loan B As Amended June 2017
Summary of Long-term debt
Long-term debt									$ 479,000,000.0	$ 796,000,000.0
Interest rate, stated percentage									3.01%	3.48%
Second Amended and Restated Credit Facility
Summary of Long-term debt
Payments of debt issuance costs				$ 8,900,000
Second Amended and Restated Revolving Loan
Summary of Long-term debt
Maximum borrowing capacity				350,000,000.0									$ 481,000,000.0	$ 350,000,000.0
Long-term line of credit									$ 0	$ 0
Incremental borrowing capacity									131,000,000				$ 131,000,000.0
Second Amended and Restated Term Loan B
Summary of Long-term debt
Maximum borrowing capacity				800,000,000.0				$ 350,000,000.0				$ 481,000,000.0
Basis spread reduction		0.25%
Loss on debt extinguishment, net		$ 300,000		$ 6,200,000
Incremental borrowing capacity												131,000,000.0
Long-term debt									479,000,000	796,000,000
Repayment of debt	315,000,000.0
Annual interest cost savings from borrowing rate reduction		$ (2,000,000.0)
Second Amended and Restated Term Loan B \| Interest Rate Swap
Summary of Long-term debt
Number of agreements \| item															2	3
Notional amount															$ 400,000,000.0	$ 300,000,000.0
Second Amended and Restated Term Loan B \| LIBOR
Summary of Long-term debt
Basis spread on variable rate		1.75%
Senior Unsecured 2024 Notes
Summary of Long-term debt
Payments of debt issuance costs							4,700,000
Loss on debt extinguishment, net								1,000,000.0
Long-term debt								949,500,000	949,490,000	1,000,000,000
Debt instrument, face amount							$ 300,000,000.0
Interest rate, stated percentage							4.875%
Periodic payment of interest					$ 24,400,000	$ 9,100,000		23,100,000
Pre-payment								$ 50,500,000
Senior Unsecured 2024 Notes Add-on
Summary of Long-term debt
Payments of debt issuance costs					3,900,000
Debt instrument, face amount					$ 700,000,000.0
Interest rate, stated percentage					4.875%
Senior Unsecured 2025 Notes
Summary of Long-term debt
Long-term debt									725,000,000
Debt instrument, face amount												$ 725,000,000.0
Interest rate, stated percentage												7.00%
Periodic payment of interest									25,400,000
Period payment of interest - first payment									35,100,000
Senior Unsecured 2025 Notes \| Six Flags Theme Parks Inc.
Summary of Long-term debt
Debt instrument, face amount	$ 725,000,000.0
Interest rate, stated percentage	7.00%
Senior Unsecured 2027 Notes
Summary of Long-term debt
Payments of debt issuance costs					$ 2,600,000
Long-term debt									$ 500,000,000	$ 500,000,000
Debt instrument, face amount					$ 500,000,000.0
Interest rate, stated percentage					5.50%