Income taxes - Income (Loss) before provision & Provision for income taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of income (loss) before provision for income taxes by jurisdiction
United States	$ 6,013,718	$ 4,431,779	$ 2,563,036
Outside United States	3,628,628	1,960,309	1,397,812
Income from operations before benefit (provision) for income taxes	9,642,346	6,392,088	3,960,848
Current tax:
United States-State and local	18,588	24,456	9,456
Outside United States	1,018,649	1,484,002	756,752
Total current tax	1,037,237	1,508,458	766,208
Deferred tax:
United States-Federal	(15,648,541)	(5,840,470)
United States-State and local	(657,779)	(352,782)
Outside United States	(160,573)	714,434	34,255
Total deferred tax	(16,466,893)	(5,478,818)	34,255
Provision for income taxes, net	(15,429,656)	(3,970,360)	800,463
Foreign Tax Receivable Expensed		700,000
Deferred Tax Reversal		500,000
Amount of deferred tax asset from which it is more likely than not that the Company would realize the benefit			29,900,000
Valuation allowance	928,701	20,561,516	28,500,000
Deferred tax liability	257,137	408,657	700,000
Deferred tax liability/ net deferred tax asset	22,673,206	$ 6,206,313	$ 700,000
Undistributed Earnings of Foreign Subsidiaries	$ 25,700,000