Stockholder's Equity - Additional Information (Detail) - USD ($)					3 Months Ended
	Mar. 02, 2020	Dec. 05, 2019	Apr. 30, 2019	Nov. 14, 2018	Mar. 31, 2020	Sep. 30, 2019	Dec. 04, 2019	Nov. 05, 2019	Mar. 31, 2019	Nov. 13, 2018	Aug. 03, 2018
Class of Stock [Line Items]
Stock repurchase program, authorized amount								$ 500,000,000			$ 500,000,000
Preferred Stock, Shares Authorized (in shares)					50,000,000				50,000,000
Preferred Stock, Shares Issued (in shares)					0				0
Preferred Stock, Shares Outstanding (in shares)					0				0
Pla-Fit Holdings, LLC
Class of Stock [Line Items]
Number of shares exchanged					2,060,443
Holdings Units
Class of Stock [Line Items]
Number of shares exchanged					2,060,443
Investor | Secondary Offering and Exchange
Class of Stock [Line Items]
Number of units held by owners (in shares)					79,927,858
Investor | Pla-Fit Holdings, LLC | Secondary Offering and Exchange
Class of Stock [Line Items]
Percentage of economic interest					92.50%
Continuing LLC Owners | Secondary Offering and Exchange
Class of Stock [Line Items]
Number of units held by owners (in shares)					6,501,477
Continuing LLC Owners | Pla-Fit Holdings, LLC | Secondary Offering and Exchange
Class of Stock [Line Items]
Percentage of economic interest					7.50%
Holdings Units
Class of Stock [Line Items]
Shares exchanged for Class A common stock					1
Class A Common Stock
Class of Stock [Line Items]
Number of shares exchanged					2,060,443
Class A Common Stock | Investor | Secondary Offering and Exchange
Class of Stock [Line Items]
Number of units held by owners (in shares)					79,927,858
Class A Common Stock | Investor | Pla-Fit Holdings, LLC | Secondary Offering and Exchange
Class of Stock [Line Items]
Percentage of voting interests acquired					92.50%
Class B Common Stock
Class of Stock [Line Items]
Shares exchanged for Class A common stock					1
Number of shares exchanged					2,060,443
Class B Common Stock | Continuing LLC Owners | Secondary Offering and Exchange
Class of Stock [Line Items]
Number of units held by owners (in shares)					6,501,477
Class B Common Stock | Continuing LLC Owners | Pla-Fit Holdings, LLC | Secondary Offering and Exchange
Class of Stock [Line Items]
Percentage of voting interests acquired					7.50%
2019 ASR Agreement
Class of Stock [Line Items]
Stock repurchase program, authorized amount							$ 300,000,000
Repurchase and retirement of common stock	$ 60,000,000	$ 240,000,000
2019 ASR Agreement | Class A Common Stock
Class of Stock [Line Items]
Stock repurchased (in shares)	666,961	3,289,924
Weighted average cost per share (in dollars per share)	$ 75.82
2018 ASR Agreement
Class of Stock [Line Items]
Stock repurchase program, authorized amount										$ 300,000,000
Repurchase and retirement of common stock			$ 60,000,000	$ 240,000,000
2018 ASR Agreement | Class A Common Stock
Class of Stock [Line Items]
Stock repurchased (in shares)			524,124	4,607,410		2,272,001
Weighted average cost per share (in dollars per share)			$ 58.46			$ 69.51