Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Oct. 26, 2016
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q3
Trading Symbol	PLNT
Entity Registrant Name	PLANET FITNESS, INC.
Entity Central Index Key	0001637207
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Class A Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		50,049,305
Class B Common Stock [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		48,530,085