Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings Per Common Share
Antidilutive stock options excluded from computation of diluted shares outstanding (in shares)									3,500	700	400
Calculation of earnings per common share
Net (loss) income attributable to Six Flags Entertainment Corporation common stockholders	$ (11,155)	$ 179,833	$ 79,519	$ (69,132)	$ 79,422	$ 184,417	$ 74,502	$ (62,345)	$ 179,065	$ 275,996	$ 273,816
Weighted-average common shares outstanding:
Weighted-average common shares outstanding-basic (in shares)									84,348	84,100	86,802
Effect of dilutive stock options and restricted stock units (in shares)									620	1,345	1,692
Weighted-average common shares outstanding-diluted (in shares)									84,968	85,445	88,494
Earnings per share - basic (in dollars per share)	$ (0.13)	$ 2.13	$ 0.94	$ (0.82)	$ 0.94	$ 2.19	$ 0.89	$ (0.74)	$ 2.12	$ 3.28	$ 3.15
Earnings per share - diluted (in dollars per share)	$ (0.13)	$ 2.11	$ 0.94	$ (0.82)	$ 0.93	$ 2.16	$ 0.88	$ (0.74)	$ 2.11	$ 3.23	$ 3.09