Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Oct. 23, 2020
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2020
Entity Registrant Name	Six Flags Entertainment Corporation
Entity File Number	1-13703
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-3995059
Entity Address, Address Line One	1000 Ballpark Way Suite 400
Entity Address, City or Town	Arlington
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	76011
City Area Code	972
Local Phone Number	595-5000
Title of 12(b) Security	Common stock, $0.025 par value per share
Trading Symbol	SIX
Security Exchange Name	NYSE
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		84,977,079
Entity Central Index Key	0000701374
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false