Condensed consolidated statement of changes in equity (deficit) (Unaudited) - 6 months ended Jun. 30, 2018 - USD ($) shares in Thousands, $ in Thousands	Total	Accumulated other comprehensive (loss) income	Additional paid- in capital	Accumulated deficit	Non-controlling interests	Class A Common Stock	Class A Common Stock Common stock	Class B Common Stock	Class B Common Stock Common stock
Beginning balance (in shares) at Dec. 31, 2017						87,188	87,188	11,193	11,193
Beginning balance at Dec. 31, 2017	$ (136,937)	$ (648)	$ 12,118	$ (130,966)	$ (17,451)		$ 9		$ 1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	53,912			45,755	8,157
Equity-based compensation expense	2,687		2,690	(3)
Exchanges of Class B common stock, shares issued							713		(713)
Exchanges of Class B common stock	0		(1,471)		1,471
Retirement of Class B common stock (in shares)									(9)
Retirement of Class B common stock	0
Exercise of stock options and vesting of restricted share units (in shares)							31
Exercise of stock options and vesting of restricted share units	400		400
Tax benefit arrangement liability and deferred taxes arising from exchanges of Class B common stock	1,007		1,007
Forfeiture of dividend equivalents	58			58
Distributions paid to members of Pla-Fit Holdings	(3,503)				(3,503)
Cumulative effect adjustment (Note 15)	(9,192)			(9,192)
Other comprehensive income	320	263			57
Ending balance (in shares) at Jun. 30, 2018						87,932	87,932	10,471	10,471
Ending balance at Jun. 30, 2018	$ (91,248)	$ (385)	$ 14,744	$ (94,348)	$ (11,269)		$ 9		$ 1