Revenue recognition - Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 289,431	$ 113,080	$ 113,080
Restricted cash	30,708		0
Accounts receivable, net	38,960	37,272	37,272
Due from related parties	0	3,020	3,020
Inventory	5,122	2,692	2,692
Restricted assets – national advertising fund	0	499	499
Prepaid expenses	4,947	3,929	3,929
Other receivables	12,548	9,562	9,562
Other current assets		6,947
Income tax receivable	6,824		6,947
Total current assets	388,540	177,001	177,001
Property and equipment, net	114,367	83,327	83,327
Intangible assets, net	234,330	235,657	235,657
Goodwill	199,513	176,981	176,981	$ 176,981
Deferred income taxes	414,841	411,067	407,782
Other assets, net	1,825	11,717	11,717
Total assets	1,353,416	1,095,750	1,092,465
Current liabilities:
Current maturities of long-term debt	12,000	7,185	7,185
Accounts payable	30,428	28,648	28,648
Accrued expenses	32,384	18,590	18,590
Equipment deposits	7,908	6,498
Restricted liabilities – national advertising fund	0	490	490
Deferred revenue, current	23,488	18,319	19,083
Payable pursuant to tax benefit arrangements, current	24,765	31,062
Other current liabilities	430	474	474
Total current liabilities	131,403	111,266	112,030
Long-term debt, net of current maturities	1,160,127	696,576	696,576
Deferred rent, net of current portion	10,083	6,127	6,127
Deferred revenue, net of current portion	26,374	21,681	8,440
Deferred tax liabilities	2,303	1,629	1,629
Payable pursuant to tax benefit arrangements, net of current portion	404,468	400,298
Other liabilities	1,447	4,302	4,302
Total noncurrent liabilities	1,604,802	1,130,613	1,117,372
Stockholders' equity (deficit):
Accumulated other comprehensive loss	94	(648)	(648)
Additional paid in capital	19,732	12,118	12,118
Accumulated deficit	(394,410)	(140,158)	(130,966)
Total stockholders' deficit attributable to Planet Fitness, Inc.	(374,574)	(128,678)	(119,486)
Non-controlling interests	(8,215)	(17,451)	(17,451)
Total stockholders' deficit	(382,789)	(146,129)	(136,937)	$ (214,755)	$ (1,080)
Total liabilities and stockholders' deficit	1,353,416	1,095,750	1,092,465
Class A Common Stock
Stockholders' equity (deficit):
Common stock, value	9	9	9
Class B Common Stock
Stockholders' equity (deficit):
Common stock, value	1	$ 1	1
Total adjustments | Accounting Standards Update 2014-09
Current assets:
Cash and cash equivalents	0		0
Restricted cash	0
Accounts receivable, net	0		0
Due from related parties	0		0
Inventory	0		0
Restricted assets – national advertising fund	425		0
Prepaid expenses	0		0
Other receivables	0		0
Other current assets			0
Income tax receivable	(1,437)
Total current assets	(1,012)		0
Property and equipment, net	0		0
Intangible assets, net	0		0
Goodwill	0		0
Deferred income taxes	(3,285)		3,285
Other assets, net	0		0
Total assets	(4,297)		3,285
Current liabilities:
Current maturities of long-term debt	0		0
Accounts payable	0		0
Accrued expenses	0		0
Equipment deposits	0		0
Restricted liabilities – national advertising fund	0		0
Deferred revenue, current	118		(764)
Payable pursuant to tax benefit arrangements, current	0		0
Other current liabilities	0		0
Total current liabilities	118		(764)
Long-term debt, net of current maturities	0		0
Deferred rent, net of current portion	0		0
Deferred revenue, net of current portion	(18,448)		13,241
Deferred tax liabilities	0		0
Payable pursuant to tax benefit arrangements, net of current portion	0		0
Other liabilities	0		0
Total noncurrent liabilities	(18,448)		13,241
Stockholders' equity (deficit):
Accumulated other comprehensive loss	0		0
Additional paid in capital	0		0
Accumulated deficit	13,391		(9,192)
Total stockholders' deficit attributable to Planet Fitness, Inc.	13,391		(9,192)
Non-controlling interests	642		0
Total stockholders' deficit	14,033		(9,192)
Total liabilities and stockholders' deficit	(4,297)		3,285
Total adjustments | Accounting Standards Update 2014-09 | Class A Common Stock
Stockholders' equity (deficit):
Common stock, value	0		0
Total adjustments | Accounting Standards Update 2014-09 | Class B Common Stock
Stockholders' equity (deficit):
Common stock, value	0		0
Amounts under Previous Standards
Current assets:
Cash and cash equivalents	289,431		113,080
Restricted cash	30,708
Accounts receivable, net	38,960		37,272
Due from related parties	0		3,020
Inventory	5,122		2,692
Restricted assets – national advertising fund	425		499
Prepaid expenses	4,947		3,929
Other receivables	12,548		9,562
Other current assets			6,947
Income tax receivable	5,387
Total current assets	387,528		177,001
Property and equipment, net	114,367		83,327
Intangible assets, net	234,330		235,657
Goodwill	199,513		176,981
Deferred income taxes	411,556		407,782
Other assets, net	1,825		11,717
Total assets	1,349,119		1,092,465
Current liabilities:
Current maturities of long-term debt	12,000		7,185
Accounts payable	30,428		28,648
Accrued expenses	32,384		18,590
Equipment deposits	7,908		6,498
Restricted liabilities – national advertising fund	0		490
Deferred revenue, current	23,606		19,083
Payable pursuant to tax benefit arrangements, current	24,765		31,062
Other current liabilities	430		474
Total current liabilities	131,521		112,030
Long-term debt, net of current maturities	1,160,127		696,576
Deferred rent, net of current portion	10,083		6,127
Deferred revenue, net of current portion	7,926		8,440
Deferred tax liabilities	2,303		1,629
Payable pursuant to tax benefit arrangements, net of current portion	404,468		400,298
Other liabilities	1,447		4,302
Total noncurrent liabilities	1,586,354		1,117,372
Stockholders' equity (deficit):
Accumulated other comprehensive loss	94		(648)
Additional paid in capital	19,732		12,118
Accumulated deficit	(381,019)		(130,966)
Total stockholders' deficit attributable to Planet Fitness, Inc.	(361,183)		(119,486)
Non-controlling interests	(7,573)		(17,451)
Total stockholders' deficit	(368,756)		(136,937)
Total liabilities and stockholders' deficit	1,349,119		1,092,465
Amounts under Previous Standards | Class A Common Stock
Stockholders' equity (deficit):
Common stock, value	9		9
Amounts under Previous Standards | Class B Common Stock
Stockholders' equity (deficit):
Common stock, value	$ 1		$ 1