Income Taxes - Uncertain tax positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Gross unrecognized tax benefit, beginning of the year	$ 1,754	$ 1,364
Increases related to tax positions taken during current year	519	390
Gross unrecognized tax benefit, ending balance	$ 2,273	$ 1,754