Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Aug. 01, 2018
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	PLNT
Entity Registrant Name	PLANET FITNESS, INC.
Entity Central Index Key	0001637207
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Class A Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		88,168,785
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		10,235,804