Commitments and contingencies - Acquiring bank sponsorship agreements (Details)		12 Months Ended
	Sep. 01, 2013 USD ($)	Dec. 31, 2015 USD ($) item	Dec. 31, 2014 USD ($)
Contingent liabilities
Number of acquiring bank sponsoring agreements | item		2
Employment agreements
Commitment to pay severance in event of employment termination without cause		$ 900,000	$ 800,000
Commitment to pay severance in event of employment termination upon change of control		1,100,000	$ 1,000,000
Future minimum payments under acquiring bank sponsorship agreements
2016		366,667
2017		416,667
2018		300,000
Total payments		1,083,334
Fraud related to certain credit card transactions
Contingent liabilities
Reserves posted by merchants with sponsor bank		900,000
Reserves posted by entity		300,000
Cash reserves required to be posted by merchant, entity		2,200,000
Contingent liability		0
Bank Sponsorship Agreement
Contingent liabilities
Contingent liability		0
Term of Bank Sponsorship Agreement	5 years
Bank Sponsorship Agreement | Financial Guarantee | Minimum
Contingent liabilities
Bank sponsorship agreement annual fees in year one	$ 300,000
Bank sponsorship agreement fees final year	500,000
Cost of sales | Bank Sponsorship Agreement | Financial Guarantee | Minimum
Contingent liabilities
Bank sponsorship agreement fees due	$ 1,800,000
Insurance reimbursement | Selling general and administrative expenses
Future minimum payments under acquiring bank sponsorship agreements
Gain on insurance reimbursement		$ 500,000