Goodwill and intangible assets (Tables)

12 Months Ended

Dec. 31, 2016

Goodwill and intangible assets

Schedule of changes in carrying amount of goodwill

Goodwill, gross, as of December 31, 2014	$	319,671
Impact of change in Euro exchange rate		(32,819)
Accumulated impairment losses as of December 31, 2015		—
Goodwill, net, as of December 31, 2015		286,852
Impact of change in Euro exchange rate		(10,066)
Accumulated impairment losses as of December 31, 2016		—
Goodwill, net, as of December 31, 2016	$	276,786

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

	December 31, 2016						December 31, 2015						Amortization
	Gross book		Accumulated		Net book		Gross book		Accumulated		Net book		period
	value		amortization		value		value		amortization		value		(in years)
Trademarks and patents	$	1,203,097	$	(557,794)	$	645,303	$	1,184,612	$	(472,914)	$	711,698	15	-	21
Technology		2,305,019		(2,122,848)		182,171		2,388,852		(1,722,286)		666,566		5
Intangible assets, net	$	3,508,116	$	(2,680,642)	$	827,474	$	3,573,464	$	(2,195,200)	$	1,378,264

Schedule of amortization expense related to intangible assets

	Year ended December 31,
	2016		2015		2014
Amortization expense	$	570,391	$	573,116	$	707,657

Schedule of intangible amortization expense that will be charged to income and is estimated on the basis of book value

Intangible amortization expense that will be charged to income for the subsequent five years and thereafter is estimated on the December 31, 2016 book value, as follows:

2017	$	261,530
2018		78,392
2019		75,406
2020		66,291
2021		57,181
Thereafter		288,674
Total	$	827,474