Segment information - Concentration of revenue by customer by geographical region (Details) - item	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Payment processing services
Revenue concentration
Number of Individual Customers with Revenue Greater than Specified Percentage of Segment Revenue	0
Revenue | Geographical concentration risk | Multi-currency processing services | APAC | Customer A
Revenue concentration
Concentration risk (as a percent)	57.00%	58.00%	61.00%
Revenue | Geographical concentration risk | Multi-currency processing services | Americas | Customer D
Revenue concentration
Concentration risk (as a percent)	21.00%	12.00%	20.00%
Revenue | Geographical concentration risk | Multi-currency processing services | Americas | Customer E
Revenue concentration
Concentration risk (as a percent)		12.00%	17.00%
Revenue | Geographical concentration risk | Multi-currency processing services | Americas | Customer F
Revenue concentration
Concentration risk (as a percent)		18.00%	23.00%
Revenue | Geographical concentration risk | Multi-currency processing services | Americas | Customer I
Revenue concentration
Concentration risk (as a percent)	12.00%
Revenue | Geographical concentration risk | Multi-currency processing services | Americas | Customer J
Revenue concentration
Concentration risk (as a percent)	11.00%
Revenue | Geographical concentration risk | Multi-currency processing services | EMEA | Customer C
Revenue concentration
Concentration risk (as a percent)	60.00%	42.00%	60.00%
Revenue | Geographical concentration risk | Multi-currency processing services | EMEA | Customer H
Revenue concentration
Concentration risk (as a percent)	35.00%	58.00%	40.00%
Revenue | Customer concentration risk | Customer A
Revenue concentration
Concentration risk (as a percent)	17.00%	18.00%	21.00%
Revenue | Customer concentration risk | Customer H
Revenue concentration
Concentration risk (as a percent)		11.00%
Revenue | Customer concentration risk | Customer G
Revenue concentration
Concentration risk (as a percent)	12.00%
Revenue | Customer concentration risk | Multi-currency processing services | Customer B
Revenue concentration
Concentration risk (as a percent)	15.00%
Revenue | Customer concentration risk | Multi-currency processing services | Customer G
Revenue concentration
Concentration risk (as a percent)	30.00%