Stock-based compensation expense (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock-based expense
Total stock-based compensation expense	$ 248,647	$ 576,931	$ 574,519	$ 1,180,899
Processing and service costs
Stock-based expense
Total stock-based compensation expense	27,145	50,255	69,580	99,061
Selling general and administrative expenses
Stock-based expense
Total stock-based compensation expense	$ 221,502	526,676	504,939	1,081,838
Stock options
Stock-based expense
Options granted (in shares)	34,000
Fair value of options granted	$ 53,000
Requisite service period	36 months
Total stock-based compensation expense	$ 155,717	267,833	383,223	549,229
Restricted stock
Stock-based expense
Awards granted (in shares)	5,000
Fair value of awards granted	$ 21,000
Requisite service period	36 months
Total stock-based compensation expense	$ 92,930	$ 309,098	$ 191,296	$ 631,670
Restricted stock | Directors
Stock-based expense
Awards granted (in shares)	0.1
Fair value of awards granted	$ 200,000
Requisite service period	12 months