Condensed consolidated statement of changes in equity (deficit) (Unaudited) - 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, 2018							83,584		9,448
Beginning balance at Dec. 31, 2018	$ (382,789)	$ 94	$ 19,732	$ (394,410)	$ (8,215)		$ 9		$ 1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	31,639			27,409	4,230
Equity-based compensation expense	1,315		1,315
Exchanges of Class B common stock, shares issued (in shares)							859		(859)
Exchanges of Class B common stock			(1,172)		1,172
Exercise of stock options, vesting of restricted share units and ESPP share purchase (in shares)							20
Exercise of stock options, vesting of restricted share units and ESPP share purchase	505		505
Tax benefit arrangement liability and deferred taxes arising from exchanges of Class B common stock	2,196		2,196
Non-cash adjustments to VIEs	(3,407)				(3,407)
Distributions paid to members of Pla-Fit Holdings	(1,842)				(1,842)
Cumulative effect adjustment	(1,713)			(1,713)
Other comprehensive income	54	54
Ending balance (in shares) at Mar. 31, 2019							84,463		8,589
Ending balance at Mar. 31, 2019	(354,042)	148	22,576	(368,714)	(8,062)		$ 9		$ 1
Beginning balance (in shares) at Dec. 31, 2019						78,525	78,525	8,562	8,562
Beginning balance at Dec. 31, 2019	(707,754)	303	29,820	(736,587)	(1,299)		$ 8		$ 1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	10,383			8,607	1,776
Equity-based compensation expense	947		947
Exchanges of Class B common stock, shares issued (in shares)							2,061		(2,061)
Exchanges of Class B common stock			(956)		956
Exercise of stock options, vesting of restricted share units and ESPP share purchase (in shares)							9
Exercise of stock options, vesting of restricted share units and ESPP share purchase	459		459
Repurchase/Retirement of common stock (in shares)							(667)
Tax benefit arrangement liability and deferred taxes arising from exchanges of Class B common stock	6,190		6,190
Non-cash adjustments to VIEs	(219)				(219)
Distributions paid to members of Pla-Fit Holdings	(1,600)				(1,600)
Non-cash adjustments to VIEs	34			34
Other comprehensive income	(609)	(609)
Ending balance (in shares) at Mar. 31, 2020						79,928	79,928	6,501	6,501
Ending balance at Mar. 31, 2020	$ (692,169)	$ (306)	$ 36,460	$ (727,946)	$ (386)		$ 8		$ 1