Income Taxes - Schedule of Future Payments Under Tax Benefit Arrangements (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Remainder of 2019	$ 24,765
2020	26,284
2021	26,744
2022	27,276
2023	27,790
Thereafter	316,631
Total	$ 449,490	$ 429,233

Income taxes projected future payments under tax benefit arrangements liability.

No definition available.

Name:	plnt_IncomeTaxesProjectedFuturePaymentsUnderTaxBenefitArrangementsLiability
Namespace Prefix:	plnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Income taxes projected future payments under tax benefit arrangements liability remainder of fiscal year.

No definition available.

Name:	plnt_IncomeTaxesProjectedFuturePaymentsUnderTaxBenefitArrangementsLiabilityRemainderOfFiscalYear
Namespace Prefix:	plnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Income taxes projected future payments under tax benefit arrangements liability year five.

No definition available.

Name:	plnt_IncomeTaxesProjectedFuturePaymentsUnderTaxBenefitArrangementsLiabilityYearFive
Namespace Prefix:	plnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Income taxes projected future payments under tax benefit arrangements liability year four.

No definition available.

Name:	plnt_IncomeTaxesProjectedFuturePaymentsUnderTaxBenefitArrangementsLiabilityYearFour
Namespace Prefix:	plnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Income taxes projected future payments under tax benefit arrangements liability year thereafter.

No definition available.

Name:	plnt_IncomeTaxesProjectedFuturePaymentsUnderTaxBenefitArrangementsLiabilityYearThereafter
Namespace Prefix:	plnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Income taxes projected future payments under tax benefit arrangements liability year three.

No definition available.

Name:	plnt_IncomeTaxesProjectedFuturePaymentsUnderTaxBenefitArrangementsLiabilityYearThree
Namespace Prefix:	plnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Income taxes projected future payments under tax benefit arrangements liability year two.

No definition available.

Name:	plnt_IncomeTaxesProjectedFuturePaymentsUnderTaxBenefitArrangementsLiabilityYearTwo
Namespace Prefix:	plnt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

No definition available.

Name:	us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration