General - Basis of Presentation - Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Common Share
Antidilutive stock options excluded from computation of diluted shares outstanding (in shares)	5,811,000	3,554,000	5,811,000	3,595,000
Calculation of earnings per common share
Net income (loss) attributable to Six Flags Entertainment Corporation	$ (116,172)	$ 179,833	$ (337,612)	$ 190,220
Weighted-average common shares outstanding:
Weighted-average common shares outstanding-basic (in shares)	84,829,000	84,413,000	84,730,000	84,276,000
Effect of dilutive stock options and restricted stock units (in shares)		632,000		662,000
Weighted-average common shares outstanding-diluted (in shares)	84,829,000	85,045,000	84,730,000	84,938,000
(Loss) earnings per share - basic (in dollars per share)	$ (1.37)	$ 2.13	$ (3.98)	$ 2.26
(Loss) earnings per share - diluted (in dollars per share)	$ (1.37)	$ 2.11	$ (3.98)	$ 2.24