Goodwill and intangible assets (Tables)

6 Months Ended

Jun. 30, 2017

Goodwill and intangible assets

Schedule of changes in carrying amount of goodwill

Goodwill, gross, as of December 31, 2016	$	276,786
Impact of change in Euro exchange rate		23,633
Accumulated impairment losses as of June 30, 2017		—
Goodwill, net, as of June 30, 2017	$	300,419

Schedule of the gross book value, accumulated amortization and amortization periods of intangible assets

	As of June 30, 2017						As of December 31, 2016						Amortization
	Gross book		Accumulated		Net book		Gross book		Accumulated		Net book		period
	value		amortization		value		value		amortization		value		(in years)
Trademarks and patents	$	1,221,339	$	(598,623)	$	622,716	$	1,203,097	$	(557,794)	$	645,303	15	-	21
Technology		2,501,834		(2,501,834)		—		2,305,019		(2,122,848)		182,171		5
Intangible assets, net	$	3,723,173	$	(3,100,457)	$	622,716	$	3,508,116	$	(2,680,642)	$	827,474

Schedule of amortization expense related to intangible assets

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2017		2016		2017		2016
Amortization expense	$	88,764	$	145,880	$	225,191	$	288,018