Business organization - Additional Information (Detail)						1 Months Ended					12 Months Ended
	May 10, 2017 $ / shares shares	Mar. 14, 2017 $ / shares shares	Nov. 22, 2016 $ / shares shares	Sep. 28, 2016 $ / shares shares	Jun. 28, 2016 $ / shares shares	May 31, 2017 $ / shares shares	Mar. 31, 2017 $ / shares shares	Nov. 30, 2016 $ / shares shares	Sep. 30, 2016 $ / shares shares	Jun. 30, 2016 $ / shares shares	Dec. 31, 2018 member store state segment shares	Dec. 31, 2017 store shares	Dec. 31, 2016 store	Dec. 31, 2015 store	Aug. 05, 2015
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of members | member											12,500,000
Number of owned and franchised locations | store											1,742	1,518	1,313	1,124
Number of states in which entity operates | state											50
Number of reportable segments | segment											3
Continuing LLC Owners
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Stock issued during period, shares, conversion of units (in shares)											1,736,020	4,762,943
Percentage of economic interest (in percentage)											10.20%
Class A Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of stock issued during period (in shares)	16,085,510	15,000,000	15,000,000	8,000,000	11,500,000						1,736,020	4,762,943
Share price (in usd per share) | $ / shares	$ 20.28	$ 20.44	$ 23.22	$ 19.62	$ 16.50
Class A Common Stock | Continuing LLC Owners
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of stock issued during period (in shares)	10,869,819	10,209,242	10,136,285	5,406,019	7,891,160						1,736,020	4,762,943
Number of shares exchanged (in shares)											1,736,020	25,842,004
Class A Common Stock | Direct TSG Investors
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of stock issued during period (in shares)	5,215,691	4,790,758	4,863,715	2,593,981	3,608,840
Class A Common Stock | Secondary Offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of stock issued during period (in shares)						16,085,510	15,000,000	15,000,000	8,000,000	11,500,000
Share price (in usd per share) | $ / shares						$ 20.28	$ 20.44	$ 23.22	$ 19.62	$ 16.50
Class A Common Stock | Secondary Offering | Continuing LLC Owners
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of stock issued during period (in shares)								10,136,285	5,406,019	7,891,160
Class A Common Stock | Secondary Offering | Direct TSG Investors
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of stock issued during period (in shares)						5,215,691	4,790,758	4,863,715	2,593,981	3,608,840
Class A Common Stock | Secondary Offering | Holdings Units
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of stock issued during period (in shares)						10,869,819	10,209,242
Class B Common Stock
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of shares exchanged (in shares)											1,736,020	4,762,943
Class B Common Stock | Continuing LLC Owners
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of shares exchanged (in shares)	10,869,819	10,209,242	10,136,285	5,406,019	7,891,160						1,736,020	4,762,943
Class B Common Stock | Secondary Offering | Continuing LLC Owners
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of shares exchanged (in shares)								10,136,285	5,406,019	7,891,160
Class B Common Stock | Secondary Offering | Holdings Units
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of shares exchanged (in shares)						10,869,819	10,209,242
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)											89.80%
Pla-Fit Holdings, LLC
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of units held by owners (in shares)	10,869,819	10,209,242	10,136,285	5,406,019	7,891,160						1,736,020	4,762,943
Pla-Fit Holdings, LLC | Secondary Offering
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Number of units held by owners (in shares)						10,869,819	10,209,242	10,136,285	5,406,019	7,891,160
Pla-Fit Holdings, LLC | Planet Intermediate, LLC
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Percentage of ownership (in percentage)															100.00%
Planet Intermediate, LLC | Planet Fitness Holdings, LLC
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Percentage of ownership (in percentage)															100.00%