Consolidated statements of operations - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Total revenue	$ 174,359	$ 136,656	$ 140,550	$ 121,333	$ 134,028	$ 97,496	$ 107,316	$ 91,102	$ 572,898	$ 429,942	$ 378,241
Operating costs and expenses:
Cost of revenue									162,646	129,266	122,317
Store operations									75,005	60,657	60,121
Selling, general and administrative									72,446	60,369	50,008
National advertising fund expense									42,619	0	0
Depreciation and amortization									35,260	31,761	31,502
Other (gain) loss									878	353	(1,369)
Total operating costs and expenses									388,854	282,406	262,579
Income from operations	52,742	43,573	48,811	38,918	42,277	33,954	38,250	33,055	184,044	147,536	115,662
Other income (expense), net:
Interest income									4,681	54	21
Interest expense									(50,746)	(35,337)	(27,146)
Other income (expense), net									(6,175)	316,928	1,371
Total other expense, net									(52,240)	281,645	(25,754)
Income before income taxes									131,804	429,181	89,908
Provision for income taxes									28,642	373,580	18,661
Net income	28,779	20,472	30,418	23,493	829	18,902	18,004	17,866	103,162	55,601	71,247
Less net income attributable to non-controlling interests									15,141	22,455	49,747
Net income attributable to Planet Fitness, Inc.	$ 24,796	$ 17,471	$ 25,874	$ 19,880	$ (3,453)	$ 15,345	$ 12,412	$ 8,842	$ 88,021	$ 33,146	$ 21,500
Class A Common Stock
Net income attributable to Planet Fitness, Inc.
Basic (usd per share)	$ 0.29	$ 0.20	$ 0.30	$ 0.23	$ (0.04)	$ 0.18	$ 0.16	$ 0.14	$ 1.01	$ 0.42	$ 0.50
Diluted (usd per share)	$ 0.29	$ 0.20	$ 0.29	$ 0.23	$ (0.04)	$ 0.18	$ 0.16	$ 0.14	$ 1.00	$ 0.42	$ 0.50
Weighted-average shares of Class A common stock outstanding:
Basic (shares)									87,235,021	78,910,390	43,300,288
Diluted (shares)									87,674,903	78,971,550	43,304,685
Franchise
Revenue:
Total revenue									$ 175,314	$ 131,983	$ 97,374
Commission income
Revenue:
Total revenue									6,632	18,172	19,114
National advertising fund revenue
Revenue:
Total revenue									42,194	0	0
Corporate-owned stores
Revenue:
Total revenue									138,599	112,114	104,721
Equipment
Revenue:
Total revenue									$ 210,159	$ 167,673	$ 157,032