Income Taxes - Uncertain tax positions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Movement in uncertain tax positions
Gross increase — tax position in prior periods	$ 100,000	$ 100,000	$ 100,000
Gross increase - tax position in prior periods	400,000	0	0
Gross decrease — tax position in prior periods	0	0	0
Gross increase — current period tax position	0	0	0
Settlements	0	0	0
Lapse in statute of limitations	0	0	0
Foreign exchange	0	0	0
Uncertain tax positions at the end of the period	500,000	$ 100,000	$ 100,000
Interest and penalties included within uncertain tax positions	$ 0