Details of Certain Financial Statement Components - Property, plant and equipment, net (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Property, plant and equipment, net
Property, plant and equipment, gross	$ 2,109		$ 2,109		$ 2,200
Less: accumulated depreciation	(1,686)		(1,686)		(1,793)
Total property, plant and equipment, net	423		423		407
Depreciation expense	57	$ 59	111	$ 118
Furniture, machinery and equipment
Property, plant and equipment, net
Property, plant and equipment, gross	1,680		1,680		1,662
Leasehold improvements
Property, plant and equipment, net
Property, plant and equipment, gross	$ 429		$ 429		$ 538