Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	2 Months Ended	3 Months Ended								5 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Quarterly Financial Information [Line Items]
Total revenue		$ 116,419	$ 87,007	$ 91,472	$ 83,343	$ 105,845	$ 68,817	$ 78,952	$ 76,923		$ 378,241		$ 330,537		$ 279,777
Income from operations		36,068	26,153	27,831	25,610	28,793	10,338	18,667	14,304		115,662		72,102		61,539
Net income		21,948	14,863	18,091	16,345	17,240	737	11,612	8,541	$ 23,454	71,247		38,130		37,295
Net income attributable to Planet Fitness, Inc.		$ 10,575	$ 3,425	$ 4,132	$ 3,368	$ 2,485	$ (3,893)	$ 11,501	$ 8,425	$ 4,106	$ 21,500		$ 18,518		$ 36,808
Class A Common Stock [Member]
Earnings per share:
Class A - Basic	$ 0.05	$ 0.19	$ 0.08	$ 0.11	$ 0.09	$ 0.06				$ 0.11	$ 0.50	[1]	$ 0.11	[1]
Class A - Diluted	$ 0.04	$ 0.18	$ 0.08	$ 0.11	$ 0.09	$ 0.06				$ 0.11	$ 0.50	[1]	$ 0.11	[1]

[1] For the year ended December 31, 2015, represents earnings per share of Class A common stock and weighted-average shares of Class A common stock outstanding for the period from August 6, 2015 through December 31, 2015, the period following the recapitalization transactions and IPO (see Note 14).