Segment information - Information about revenue, profit and assets (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) item	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment information
Number of reportable segments | item			2
Cost of sales included in processing and services costs	$ 3,031,105	$ 2,878,088	$ 9,428,424	$ 9,902,879
Long-lived assets	6,800,000		$ 6,800,000		$ 7,000,000
Number of geographical regions in which the entity conducts its business | item			3
Net Revenue:
Net revenue	13,805,324	13,621,239	$ 39,050,592	40,409,128
Gross Profit:
Total gross profit	8,410,191	7,961,862	23,057,086	22,299,047
Income from operations before provision for income taxes:
Total gross profit	8,410,191	7,961,862	23,057,086	22,299,047
Selling, general and administrative expenses	4,621,566	5,222,560	14,590,609	15,908,166
Restructuring charges		229,121	72,742	354,389
Income from operations	3,788,625	2,510,181	8,393,735	6,036,492
Interest expense	(12,863)	(88,669)	(222,008)	(186,366)
Interest income	644	428	1,752	1,250
Other income	111,613	93,016	111,613	93,016
Total other income (expense), net	99,394	4,775	(108,643)	(92,100)
Income from operations before provision for income taxes	3,888,019	2,514,956	8,285,092	5,944,392
Operating segments
Gross Profit:
Total gross profit	11,027,474	10,306,583	31,081,197	30,305,001
Income from operations before provision for income taxes:
Total gross profit	11,027,474	10,306,583	31,081,197	30,305,001
Corporate allocated cost of sales
Gross Profit:
Total gross profit	2,617,283	2,344,721	8,024,111	8,005,954
Income from operations before provision for income taxes:
Total gross profit	2,617,283	2,344,721	8,024,111	8,005,954
Multi-currency processing services
Segment information
Cost of sales included in processing and services costs	400,000	500,000	1,400,000	1,900,000
Net Revenue:
Net revenue	9,533,253	8,175,476	26,477,123	24,768,314
Multi-currency processing services | Operating segments
Gross Profit:
Total gross profit	9,119,431	7,642,109	25,072,810	22,871,389
Income from operations before provision for income taxes:
Total gross profit	9,119,431	7,642,109	25,072,810	22,871,389
Payment processing services
Net Revenue:
Net revenue	4,272,071	5,445,763	12,573,469	15,640,814
Payment processing services | Operating segments
Gross Profit:
Total gross profit	1,908,043	2,664,474	6,008,387	7,433,612
Income from operations before provision for income taxes:
Total gross profit	1,908,043	2,664,474	6,008,387	7,433,612
APAC
Net Revenue:
Net revenue	4,320,879	3,962,539	12,558,229	11,541,521
APAC | Multi-currency processing services | Operating segments
Gross Profit:
Total gross profit	4,303,113	3,942,457	12,494,444	11,467,607
Income from operations before provision for income taxes:
Total gross profit	4,303,113	3,942,457	12,494,444	11,467,607
The Americas
Net Revenue:
Net revenue	4,099,625	2,634,887	10,295,406	7,264,448
The Americas | Multi-currency processing services | Operating segments
Gross Profit:
Total gross profit	3,904,298	2,470,294	9,703,121	6,766,889
Income from operations before provision for income taxes:
Total gross profit	3,904,298	2,470,294	9,703,121	6,766,889
EMEA
Net Revenue:
Net revenue	1,112,749	1,578,050	3,623,488	5,962,345
EMEA | Multi-currency processing services | Operating segments
Gross Profit:
Total gross profit	912,020	1,229,358	2,875,245	4,636,893
Income from operations before provision for income taxes:
Total gross profit	$ 912,020	$ 1,229,358	$ 2,875,245	$ 4,636,893