Consolidated Statements of Stockholders' Deficit - USD ($) $ in Thousands	Common stock	Capital in excess of par value	Accumulated deficit	Accumulated other comprehensive loss	Total
Beginning balance at Dec. 31, 2018	$ 2,099	$ 1,037,640	$ (1,611,334)	$ (71,498)	$ (643,093)
Beginning balance (in shares) at Dec. 31, 2018	83,962,182
Increase (Decrease) in Stockholders' Deficit
Issuance of common stock	$ 13	16,173			16,186
Issuance of common stock (in shares)	528,330
Stock-based compensation		11,347			11,347
Dividends declared to common shareholders			(207,325)		(207,325)
Repurchase of common stock		(52)			(52)
Repurchase of common stock (in shares)	(882)
Employee stock purchase plan	$ 1	1,204			1,205
Employee stock purchase plan (in shares)	26,937
Fresh start valuation adjustment for partnership park units purchased			45		45
Net income (loss) attributable to Six Flags Entertainment Corporation			190,220		190,220
Net other comprehensive income (loss), net of tax				(3,720)	(3,720)
Ending balance at Sep. 30, 2019	$ 2,113	1,066,312	(1,628,394)	(75,218)	(635,187)
Ending balance (in shares) at Sep. 30, 2019	84,516,567
Beginning balance at Jun. 30, 2019	$ 2,108	1,058,675	(1,738,955)	(71,635)	(749,807)
Beginning balance (in shares) at Jun. 30, 2019	84,334,531
Increase (Decrease) in Stockholders' Deficit
Issuance of common stock	$ 5	3,782			3,787
Issuance of common stock (in shares)	182,851
Stock-based compensation		3,903			3,903
Dividends declared to common shareholders			(69,272)		(69,272)
Repurchase of common stock		(48)			(48)
Repurchase of common stock (in shares)	(815)
Net income (loss) attributable to Six Flags Entertainment Corporation			179,833		179,833
Net other comprehensive income (loss), net of tax				(3,583)	(3,583)
Ending balance at Sep. 30, 2019	$ 2,113	1,066,312	(1,628,394)	(75,218)	(635,187)
Ending balance (in shares) at Sep. 30, 2019	84,516,567
Beginning balance at Dec. 31, 2019	$ 2,116	1,066,223	(1,709,747)	(74,710)	(716,118)
Beginning balance (in shares) at Dec. 31, 2019	84,633,845
Increase (Decrease) in Stockholders' Deficit
Issuance of common stock	$ 7	1,146			1,153
Issuance of common stock (in shares)	277,532
Stock-based compensation		18,207			18,207
Dividends declared to common shareholders			(21,165)		(21,165)
Repurchase of common stock		(54)			(54)
Repurchase of common stock (in shares)	(2,291)
Employee stock purchase plan	$ 1	717			718
Employee stock purchase plan (in shares)	41,532
Fresh start valuation adjustment for partnership park units purchased			924		924
Change in redemption value of partnership units		(18)			(18)
Net income (loss) attributable to Six Flags Entertainment Corporation			(337,612)		(337,612)
Net other comprehensive income (loss), net of tax				(22,740)	(22,740)
Ending balance at Sep. 30, 2020	$ 2,124	1,086,221	(2,067,600)	(97,450)	(1,076,705)
Ending balance (in shares) at Sep. 30, 2020	84,950,618
Beginning balance at Jun. 30, 2020	$ 2,119	1,077,948	(1,951,428)	(99,421)	(970,782)
Beginning balance (in shares) at Jun. 30, 2020	84,757,286
Increase (Decrease) in Stockholders' Deficit
Issuance of common stock	$ 5	414			419
Issuance of common stock (in shares)	195,468
Stock-based compensation		7,907			7,907
Repurchase of common stock		(48)			(48)
Repurchase of common stock (in shares)	(2,136)
Net income (loss) attributable to Six Flags Entertainment Corporation			(116,172)		(116,172)
Net other comprehensive income (loss), net of tax				1,971	1,971
Ending balance at Sep. 30, 2020	$ 2,124	$ 1,086,221	$ (2,067,600)	$ (97,450)	$ (1,076,705)
Ending balance (in shares) at Sep. 30, 2020	84,950,618