Business Organization - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2020 member store state segment	Mar. 31, 2020 store	Dec. 31, 2019 store	Jun. 30, 2019 store	Mar. 31, 2019 store	Dec. 31, 2018 store	Aug. 05, 2015
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of owned and franchised locations	2,059	2,039	2,001	1,859	1,806	1,742
Number of states in which entity operates | state	50
Number of stores reopened	1,490
Number of reportable segments | segment	3
Pla-Fit Holdings, LLC
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Percentage of ownership (in percentage)	100.00%						100.00%
Percentage of economic interest (in percentage)	92.50%
Pla-Fit Holdings, LLC | Holdings Units
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Percentage of economic interest (in percentage)	7.50%
Planet Intermediate, LLC | Pla-Fit Holdings, LLC
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Percentage of ownership (in percentage)							100.00%
Planet Fitness Holdings, LLC | Planet Intermediate, LLC
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Percentage of ownership (in percentage)							100.00%
Minimum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of members (more than) | member	15,200,000
Franchisee-Owned Stores
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of owned and franchised locations	1,960	1,940	1,903	1,779	1,730	1,666
Number of stores reopened	1,451
Corporate-Owned Stores
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of owned and franchised locations	99	99	98	80	76	76
Number of stores reopened	39