Revenue from contract with customers - Schedule of Deferred Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	$ 59,278	$ 62,054
Long-term portion of deferred revenue	32,587	34,458
Current portion of deferred revenue	26,691	27,596
Prepaid membership fees
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	6,021	7,231
Enrollment fees
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	399	915
Equipment discount
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	4,013	3,796
Annual membership fees
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	12,506	12,185
Area development and franchise fees
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	$ 36,339	$ 37,927