Stockholder's Equity - Additional Information (Detail) - shares	6 Months Ended
	Jun. 30, 2018	Dec. 31, 2017
Pla-Fit Holdings, LLC
Class of Stock [Line Items]
Number of shares exchanged	713,000
Holdings Units
Class of Stock [Line Items]
Number of shares exchanged	713,000
Investor | Secondary Offering and Exchange
Class of Stock [Line Items]
Common stock, shares outstanding	87,932,160
Investor | Pla-Fit Holdings, LLC | Secondary Offering and Exchange
Class of Stock [Line Items]
Percentage of economic interest	89.40%
Continuing LLC Owners | Secondary Offering and Exchange
Class of Stock [Line Items]
Number of units held by owners (in shares)	10,470,750
Continuing LLC Owners | Pla-Fit Holdings, LLC | Secondary Offering and Exchange
Class of Stock [Line Items]
Percentage of economic interest	10.60%
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	713,000
Common stock, shares outstanding	87,932,000	87,188,000
Class A Common Stock | Investor | Secondary Offering and Exchange
Class of Stock [Line Items]
Common stock, shares outstanding	87,932,160
Class A Common Stock | Investor | Pla-Fit Holdings, LLC | Secondary Offering and Exchange
Class of Stock [Line Items]
Percentage of voting interests acquired	89.40%
Class B Common Stock
Class of Stock [Line Items]
Shares exchanged for Class A common stock	1
Number of shares exchanged	713,000
Common stock, shares outstanding	10,471,000	11,193,000
Class B Common Stock | Continuing LLC Owners | Secondary Offering and Exchange
Class of Stock [Line Items]
Number of units held by owners (in shares)	10,470,750
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	10.60%