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 (loss) income	71,466			62,253	9,213
Equity-based compensation expense	2,279		2,279
Exchanges of Class B common stock (in shares)							866		(866)
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)							69
Exercise of stock options, vesting of restricted share units and ESPP share purchase	1,209		1,209
Repurchase and retirement of common stock (in shares)							(524)
Repurchase and retirement of common stock	(1)		64		(64)		$ (1)
Tax benefit arrangement liability and deferred taxes arising from exchanges of Class B common stock	2,383		2,383
Non-cash adjustments to VIEs	(3,621)				(3,621)
Distributions paid to members of Pla-Fit Holdings	(3,742)				(3,742)
Cumulative effect adjustment	(1,713)			(1,713)
Other comprehensive income	157	157
Ending balance (in shares) at Jun. 30, 2019							83,995		8,582
Ending balance at Jun. 30, 2019	(314,372)	251	24,495	(333,870)	(5,257)		$ 8		$ 1
Beginning balance (in shares) at Mar. 31, 2019							84,463		8,589
Beginning balance at Mar. 31, 2019	(354,042)	148	22,576	(368,714)	(8,062)		$ 9		$ 1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	39,827			34,844	4,983
Equity-based compensation expense	964		964
Exchanges of Class B common stock (in shares)							7		(7)
Exercise of stock options, vesting of restricted share units and ESPP share purchase (in shares)							49
Exercise of stock options, vesting of restricted share units and ESPP share purchase	704		704
Repurchase and retirement of common stock (in shares)							(524)
Repurchase and retirement of common stock	(1)		64		(64)		$ (1)
Tax benefit arrangement liability and deferred taxes arising from exchanges of Class B common stock	187		187
Non-cash adjustments to VIEs	(214)				(214)
Distributions paid to members of Pla-Fit Holdings	(1,900)				(1,900)
Other comprehensive income	103	103
Ending balance (in shares) at Jun. 30, 2019							83,995		8,582
Ending balance at Jun. 30, 2019	(314,372)	251	24,495	(333,870)	(5,257)		$ 8		$ 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 (loss) income	(21,602)			(20,570)	(1,032)
Equity-based compensation expense	2,493		2,493
Exchanges of Class B common stock (in shares)							2,062		(2,062)
Exchanges of Class B common stock			(956)		956
Exercise of stock options, vesting of restricted share units and ESPP share purchase (in shares)							74
Exercise of stock options, vesting of restricted share units and ESPP share purchase	1,353		1,353
Repurchase and 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	(438)				(438)
Distributions paid to members of Pla-Fit Holdings	(1,600)				(1,600)
Other	18			18
Other comprehensive income	(360)	(360)
Ending balance (in shares) at Jun. 30, 2020						79,994	79,994	6,500	6,500
Ending balance at Jun. 30, 2020	(721,700)	(57)	38,900	(757,139)	(3,413)		$ 8		$ 1
Beginning balance (in shares) at Mar. 31, 2020							79,928		6,501
Beginning balance at Mar. 31, 2020	(692,169)	(306)	36,460	(727,946)	(386)		$ 8		$ 1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(31,985)			(29,177)	(2,808)
Equity-based compensation expense	1,546		1,546
Exchanges of Class B common stock (in shares)							1		(1)
Exercise of stock options, vesting of restricted share units and ESPP share purchase (in shares)							65
Exercise of stock options, vesting of restricted share units and ESPP share purchase	894		894
Non-cash adjustments to VIEs	(219)				(219)
Other	(16)			(16)
Other comprehensive income	249	249
Ending balance (in shares) at Jun. 30, 2020						79,994	79,994	6,500	6,500
Ending balance at Jun. 30, 2020	$ (721,700)	$ (57)	$ 38,900	$ (757,139)	$ (3,413)		$ 8		$ 1