Intangible assets other than goodwill - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 98,310	$ 99,721
Product Certifications
Acquired Finite-Lived Intangible Assets [Line Items]
Capitalized finited lived intangible assets	30,035	39,272
Patents
Acquired Finite-Lived Intangible Assets [Line Items]
Capitalized finited lived intangible assets	$ 77,240	88,985
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	$ 12,390	$ 4,775