Significant accounting policies (advertising costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Advertising costs [Line Items]
Advertising expense	$ 74,549	$ 78,722	$ 85,141
Maximum [Member]
Advertising costs [Line Items]
Deferred advertising costs amortization period	18 months
Reportable business segments [Member] | Small Business Services [Member]
Advertising costs [Line Items]
Deferred advertising costs amortization period	6 months
Reportable business segments [Member] | Direct Checks [Member]
Advertising costs [Line Items]
Percentage of deferred advertising costs expensed within six months	88.00%