Summary of significant accounting policies (Details 3) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2013
Deferred initial public offering ("IPO") costs
Minimum period for which initial public offering was likely to be postponed		90 days
Write-off of deferred IPO costs	$ 2,300,000		$ 2,346,210
Initial public offering costs	2,600,000
Due to merchants
Number of average days for which ACH funds are generally held before payment to merchant		3 days
Income taxes
Uncertain tax positions		$ 0		$ 0