Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information (Unaudited)
Revenues	$ 108,602	$ 126,327	$ 19,143	$ 102,503	$ 261,000	$ 621,180	$ 477,210	$ 128,193	$ 356,575	$ 1,487,583	$ 1,463,707
Income (loss) before income taxes	(112,782)	(131,771)	(171,911)	(106,595)	10,143	261,835	133,571	(93,789)	(523,059)	311,760	411,858
Net (loss) income attributable to Six Flags Entertainment Corporation common stockholders	$ (85,768)	$ (116,172)	$ (136,894)	$ (84,546)	$ (11,155)	$ 179,833	$ 79,519	$ (69,132)	$ (423,380)	$ 179,065	$ 275,996
Net (loss) income per weighted average common share outstanding:
(Loss) earnings per share - basic (in dollars per share)	$ (1.00)	$ (1.37)	$ (1.62)	$ (1.00)	$ (0.13)	$ 2.13	$ 0.94	$ (0.82)	$ (4.99)	$ 2.12	$ 3.28
(Loss) earnings per share - diluted (in dollars per share)	$ (1.00)	$ (1.37)	$ (1.62)	$ (1.00)	$ (0.13)	$ 2.11	$ 0.94	$ (0.82)	$ (4.99)	$ 2.11	$ 3.23