Intangible assets other than goodwill - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 92,209	$ 112,359
Net credit to cost of sales related to the amortization of contract related assets and liabilities	502,729	860,858
Product Certifications
Acquired Finite-Lived Intangible Assets [Line Items]
Capitalized finited lived intangible assets	0	120,455
Patents
Acquired Finite-Lived Intangible Assets [Line Items]
Capitalized finited lived intangible assets	$ 106,539	102,245
Patents \| Minimum
Acquired Finite-Lived Intangible Assets [Line Items]
Finited lived intangible assets, estimated useful life	7 years
Patents \| Maximum
Acquired Finite-Lived Intangible Assets [Line Items]
Finited lived intangible assets, estimated useful life	10 years
Trademarks
Acquired Finite-Lived Intangible Assets [Line Items]
Capitalized finited lived intangible assets	$ 4,144	$ 3,212