Property, plant and equipment - Summary of elements of property, plant and equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Property, plant and equipment
Subtotal	$ 67,213	$ 63,998
Less: Accumulated depreciation	(44,432)	(42,444)
Total	22,781	21,554
Land
Property, plant and equipment
Subtotal	1,255	1,255
Land improvements
Property, plant and equipment
Subtotal	$ 319	319
Land improvements \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	6 years
Land improvements \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	10 years
Buildings
Property, plant and equipment
Subtotal	$ 1,446	1,446
Buildings \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	25 years
Buildings \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	39 years
Building improvements
Property, plant and equipment
Subtotal	$ 3,624	3,569
Building improvements \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	25 years
Building improvements \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	39 years
Cylinders
Property, plant and equipment
Subtotal	$ 12,878	12,957
Cylinders \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	15 years
Cylinders \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	30 years
Equipment
Property, plant and equipment
Subtotal	$ 33,790	32,525
Equipment \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	3 years
Equipment \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	10 years
Equipment under capital lease
Property, plant and equipment
Subtotal	$ 315	315
Equipment under capital lease \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	5 years
Equipment under capital lease \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	7 years
Vehicles
Property, plant and equipment
Subtotal	$ 2,213	2,081
Vehicles \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	3 years
Vehicles \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	5 years
Lab and computer equipment, software
Property, plant and equipment
Subtotal	$ 3,304	3,304
Lab and computer equipment, software \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	2 years
Lab and computer equipment, software \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	8 years
Furniture and fixtures
Property, plant and equipment
Subtotal	$ 1,125	1,125
Furniture and fixtures \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	5 years
Furniture and fixtures \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	10 years
Leasehold improvements
Property, plant and equipment
Subtotal	$ 865	865
Leasehold improvements \| Minimum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	3 years
Leasehold improvements \| Maximum
Property, plant and equipment
Property, plant and equipment, Estimated Lives	5 years
Construction-in-progress
Property, plant and equipment
Subtotal	$ 6,079	$ 4,237

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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