Corporate-owned and Franchisee-owned Stores - Schedule of Changes in Corporate-owned and Franchisee-owned Stores (Detail) - Store		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Franchisor Disclosure [Line Items]
Stores operated at beginning of period		1,206	1,014	1,124	918
New stores opened		37	26	121	125
Stores debranded or consolidated	[1]	(1)		(3)	(3)
Stores operated at end of period		1,242	1,040	1,242	1,040
Franchisee-Owned Stores [Member]
Franchisor Disclosure [Line Items]
Stores operated at beginning of period		1,148	956	1,066	863
New stores opened		37	26	121	122
Stores debranded or consolidated	[1]	(1)		(3)	(3)
Stores operated at end of period		1,184	982	1,184	982
Corporate-Owned Stores [Member]
Franchisor Disclosure [Line Items]
Stores operated at beginning of period		58	58	58	55
New stores opened					3
Stores operated at end of period		58	58	58	58

[1] The term “debrand” refers to a franchisee-owned store whose right to use the Planet Fitness brand and marks has been terminated in accordance with the franchise agreement. We retain the right to prevent debranded stores from continuing to operate as fitness centers. The term “consolidated” refers to the combination of a franchisee’s store with another store located in close proximity, with our prior approval. This often coincides with an enlargement, re-equipment and/or refurbishment of the remaining store.