| Cover Page | Dec. 03, 2019 |
| Cover page. | |
| Document Type | 8-K |
| Document Period End Date | Dec. 3, 2019 |
| Entity Registrant Name | Planet Fitness, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-37534 |
| Entity Tax Identification Number | 38-3942097 |
| Entity Address, Address Line One | 4 Liberty Lane West |
| Entity Address, City or Town | Hampton |
| Entity Address, State or Province | NH |
| Entity Address, Postal Zip Code | 03842 |
| City Area Code | 603 |
| Local Phone Number | 750-0001 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Class A common stock, $0.0001 Par Value |
| Trading Symbol | PLNT |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001637207 |
| Amendment Flag | false |
