Income taxes - Income (Loss) before provision & Provision for income taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of income (loss) before provision for income taxes by jurisdiction
United States	$ 4,431,779	$ 2,563,036	$ 537,097
Outside United States	1,960,309	1,397,812	(474,222)
Income from operations before benefit (provision) for income taxes	6,392,088	3,960,848	62,875
Current tax:
United States-State and local	24,456	9,456	5,754
Outside United States	1,484,002	756,752	619,043
Total current tax	1,508,458	766,208	624,797
Deferred tax:
United States-Federal	(5,840,470)
United States-State and local	(352,782)
Outside United States	714,434	34,255	(583,928)
Total deferred tax	(5,478,818)	34,255	(583,928)
(Benefit) provision for income taxes, net	(3,970,360)	800,463	40,869
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	31,200,000
Valuation allowance	20,561,516	28,475,080	29,400,000
Deferred tax liability	408,657	653,074	1,000,000
Deferred tax liability/ net deferred tax asset	$ 6,206,313	$ 727,495	$ 800,000