Stock-based compensation expense (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Stock-based expense
Total stock-based compensation expense	$ 325,872	$ 603,968
Processing and service costs
Stock-based expense
Total stock-based compensation expense	42,435	48,806
Selling general and administrative expenses
Stock-based expense
Total stock-based compensation expense	283,437	555,162
Stock options
Stock-based expense
Total stock-based compensation expense	227,506	281,396
Restricted stock
Stock-based expense
Total stock-based compensation expense	$ 98,366	$ 322,572