Summary of significant accounting policies (Details 7) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-based expense
Total stock-based compensation expense	$ 1,263,660	$ 1,227,369	$ 1,135,047
Capitalized stock-based compensation	52,473	52,133
Stock options
Stock-based expense
Options granted (in shares)	576,700
Total stock-based compensation expense	850,727	983,810	1,135,047
Capitalized stock-based compensation	100,000
Unamortized stock-based compensation expense	813,461	1,263,133
Weighted average remaining amortization period	1 year 10 months 6 days	1 year 9 months 15 days
Restricted stock awards
Stock-based expense
Stock granted (in shares)	930,830
Total stock-based compensation expense	412,933	243,559
Unamortized stock-based compensation expense	424,795	1,624,187
Weighted average remaining amortization period	1 year 5 months 27 days	2 years 18 days
Processing and service costs
Stock-based expense
Total stock-based compensation expense	259,663	238,101	262,775
Selling, general and administrative expenses
Stock-based expense
Total stock-based compensation expense	849,640	989,268	872,272
Restructuring charge
Stock-based expense
Total stock-based compensation expense	$ 154,357