Stockholder's Equity - Additional Information (Detail) - USD ($)						1 Months Ended		3 Months Ended	9 Months Ended
	Sep. 28, 2016	Jun. 28, 2016	Aug. 11, 2015	Aug. 05, 2015	Jun. 22, 2015	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015	Aug. 06, 2015
Class Of Stock [Line Items]
Convertible stock, conversion description									Following the Merger and the Reclassification, the Company and the Continuing LLC Owners entered into an exchange agreement under which the Continuing LLC Owners (or certain permitted transferees thereof) have the right, from time to time and subject to the terms of the exchange agreement, to exchange their Holdings Units, along with a corresponding number of shares of Class B common stock, for shares of Class A common stock (or cash at the option of the Company) on a one-for-one basis, subject to customary conversion rate adjustments for stock splits, stock dividends, reclassifications and similar transactions.
Pla-Fit Holdings, LLC [Member]
Class Of Stock [Line Items]
Number of units held by owners	5,406,019	7,891,160				5,406,019	7,891,160	5,406,019	5,406,019
Continuing LLC Owners [Member] | IPO and Secondary Offering [Member]
Class Of Stock [Line Items]
Percentage of economic interest								49.40%
Number of units held by owners						48,665,585		48,665,585	48,665,585
Class A Common Stock [Member]
Class Of Stock [Line Items]
Number of stock issued during period	8,000,000	11,500,000				8,000,000	11,500,000
Common stock, shares outstanding			36,597,985			49,914,000		49,914,000	49,914,000	36,598,000	0
Share price	$ 19.62	$ 16.50				$ 19.62	$ 16.50	$ 19.62	$ 19.62
Proceeds from sale of shares	$ 0	$ 0
Class A Common Stock [Member] | Direct TSG Investors [Member]
Class Of Stock [Line Items]
Number of shares converted					26,106,930
Number of stock issued during period	2,593,981	3,608,840	5,033,945			2,593,981	3,608,840
Class A Common Stock [Member] | Direct TSG Investors [Member] | IPO and Secondary Offering [Member]
Class Of Stock [Line Items]
Number of stock issued during period								14,870,164
Percentage of economic interest								15.10%
Percentage of voting power						15.10%		15.10%	15.10%
Class A Common Stock [Member] | Continuing LLC Owners [Member]
Class Of Stock [Line Items]
Number of stock issued during period	5,406,019	7,891,160				5,406,019	7,891,160
Number of shares exchanged						5,406,019	7,891,160
Class A Common Stock [Member] | Continuing LLC Owners [Member] | Pla-Fit Holdings, LLC [Member] | IPO [Member]
Class Of Stock [Line Items]
Number of stock issued during period			10,491,055
Aggregate amount of units issued			$ 156,946,000
Class A Common Stock [Member] | Investor | IPO and Secondary Offering [Member]
Class Of Stock [Line Items]
Number of stock issued during period								35,043,641
Percentage of economic interest								35.50%
Percentage of voting power						35.50%		35.50%	35.50%
Class B Common Stock [Member]
Class Of Stock [Line Items]
Common stock, shares outstanding						48,665,000		48,665,000	48,665,000	62,112,000	0
Class B Common Stock [Member] | Continuing LLC Owners [Member]
Class Of Stock [Line Items]
Number of stock issued during period				72,602,810
Common stock dividend and voting rights description									The shares of Class B common stock have no rights to dividends or distributions, whether in cash or stock, but entitle the holder to one vote per share on matters presented to stockholders of the Company.
Number of shares exchanged	5,406,019	7,891,160				5,406,019	7,891,160
Class B Common Stock [Member] | Continuing LLC Owners [Member] | IPO and Secondary Offering [Member]
Class Of Stock [Line Items]
Percentage of voting power						49.40%		49.40%	49.40%
Number of units held by owners						48,665,585		48,665,585	48,665,585
Class B Common Stock [Member] | Continuing LLC Owners [Member] | Pla-Fit Holdings, LLC [Member]
Class Of Stock [Line Items]
Number of stock issued during period				72,602,810
Merger Agreement [Member] | Class A Common Stock [Member] | Direct TSG Investors [Member]
Class Of Stock [Line Items]
Number of shares converted					26,106,930