Commitments and Contingencies - Additional Information (Detail) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2021 USD ($) shares	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)
Loss Contingencies [Line Items]
Legal settlement				$ 65.0
Legal settlements paid			$ 32.1
Insurance proceeds from insurers		$ 12.5
Legal settlement gain		$ 12.5
Number of shares at issue in legal matter | shares	300,000
License agreement term, description	Pursuant to a license agreement (“License Agreement”) with Sesame Workshop, the Company pays a specified annual license fee, as well as a specified royalty based on revenues earned in connection with sales of licensed products, all food and beverage items utilizing the licensed elements and any events utilizing such elements if a separate fee is paid for such event.  The Company’s principal commitments pursuant to the License Agreement include, among other items, the opening of a second standalone park (“Standalone Park”) no later than mid-2021 and minimum annual capital and marketing thresholds.  After the opening of the second Standalone Park (counting the existing Sesame Place Standalone Park in Langhorne, Pennsylvania), SEA will have the option to build additional Standalone Parks in the Sesame Territory within agreed upon timelines.  The License Agreement has an initial term through December 31, 2031, with an automatic additional 15-year extension plus a five-year option added to the term of the License Agreement from December 31st of the year of each new Standalone Park opening. As of September 30, 2021, the Company estimates the combined remaining obligations for these commitments could be up to approximately $40.0 million over the remaining current term of the agreement. In October 2019, the Company announced that it planned to convert Aquatica San Diego into its second Sesame Place Standalone Park in the spring of 2021. While construction began in the fall of 2019, it was temporarily paused due to the COVID-19 pandemic. The Company has opened its Aquatica San Diego park for the 2021 operating season and currently expects to open this park rebranded as its second Sesame Place Standalone Park in 2022.
Maximum [Member]
Loss Contingencies [Line Items]
Contingent value	$ 35.0
Estimated combined remaining obligations for commitments	40.0
Minimum [Member]
Loss Contingencies [Line Items]
Contingent value	$ 30.0