Property, plant and equipment - Summary of elements of property, plant and equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Subtotal	$ 57,405	$ 53,854
Less: Accumulated depreciation	(36,837)	(33,761)
Total	20,568	20,093
Land
Property, Plant and Equipment [Line Items]
Subtotal	1,255	1,255
Land improvements
Property, Plant and Equipment [Line Items]
Subtotal	$ 319	319
Land improvements | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	6 years
Land improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	10 years
Buildings
Property, Plant and Equipment [Line Items]
Subtotal	$ 1,446	1,446
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	25 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	39 years
Building improvements
Property, Plant and Equipment [Line Items]
Subtotal	$ 3,396	3,099
Building improvements | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	25 years
Building improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	39 years
Cylinders
Property, Plant and Equipment [Line Items]
Subtotal	$ 13,315	13,272
Cylinders | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	15 years
Cylinders | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	30 years
Equipment
Property, Plant and Equipment [Line Items]
Subtotal	$ 27,258	26,653
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	3 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	10 years
Equipment under capital lease
Property, Plant and Equipment [Line Items]
Subtotal	$ 315	315
Equipment under capital lease | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	5 years
Equipment under capital lease | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	7 years
Vehicles
Property, Plant and Equipment [Line Items]
Subtotal	$ 1,773	1,773
Vehicles | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	3 years
Vehicles | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	5 years
Lab and computer equipment, software
Property, Plant and Equipment [Line Items]
Subtotal	$ 3,103	3,103
Lab and computer equipment, software | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	2 years
Lab and computer equipment, software | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	8 years
Furniture & fixtures
Property, Plant and Equipment [Line Items]
Subtotal	$ 840	837
Furniture & fixtures | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	5 years
Furniture & fixtures | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	10 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Subtotal	$ 852	852
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	3 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, Estimated Lives	5 years
Construction-in-Progress
Property, Plant and Equipment [Line Items]
Subtotal	$ 3,533	$ 930