Income Tax - Significant components of income tax expense (benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current:
Federal	$ 0	$ 0	$ 0
State	38	18	3
Foreign	0	147	74
Current	38	165	77
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	(678)	(78)	(42)
Deferred	(678)	(78)	(42)
Total:
Federal	0	0	0
State	38	18	3
Foreign	(678)	69	32
Income tax expense (benefit)	$ (640)	$ 87	$ 35