Segment information - Concentration of revenue by customer by geographical region (Details) - Revenue	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Geographical concentration risk | Multi-currency processing services | Customer I
Revenue concentration
Concentration risk (as a percent)	13.00%		10.00%
Geographical concentration risk | Multi-currency processing services | Customer J
Revenue concentration
Concentration risk (as a percent)	11.00%
Geographical concentration risk | Multi-currency processing services | APAC | Customer A
Revenue concentration
Concentration risk (as a percent)	52.00%	57.00%	56.00%	59.00%
Geographical concentration risk | Multi-currency processing services | Americas | Customer D
Revenue concentration
Concentration risk (as a percent)	19.00%		23.00%	12.00%
Geographical concentration risk | Multi-currency processing services | Americas | Customer E
Revenue concentration
Concentration risk (as a percent)		16.00%		15.00%
Geographical concentration risk | Multi-currency processing services | Americas | Customer F
Revenue concentration
Concentration risk (as a percent)		19.00%		19.00%
Geographical concentration risk | Multi-currency processing services | EMEA | Customer C
Revenue concentration
Concentration risk (as a percent)	60.00%	55.00%	62.00%	59.00%
Geographical concentration risk | Multi-currency processing services | EMEA | Customer H
Revenue concentration
Concentration risk (as a percent)	39.00%	45.00%	37.00%	41.00%
Customer concentration risk | Customer A
Revenue concentration
Concentration risk (as a percent)	15.00%	19.00%	16.00%	20.00%
Customer concentration risk | Customer C
Revenue concentration
Concentration risk (as a percent)			10.00%	10.00%
Customer concentration risk | Customer G
Revenue concentration
Concentration risk (as a percent)	12.00%		11.00%
Customer concentration risk | Multi-currency processing services | Customer B
Revenue concentration
Concentration risk (as a percent)	16.00%	14.00%	15.00%	15.00%
Customer concentration risk | Multi-currency processing services | Customer G
Revenue concentration
Concentration risk (as a percent)	29.00%	24.00%	28.00%	22.00%