Significant accounting policies (advertising costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Advertising costs [Line Items]
Advertising expense	$ 85,141	$ 87,396	$ 91,937
Maximum [Member]
Advertising costs [Line Items]
Deferred advertising costs amortization period	18 months
Small Business Services [Member] | Actual [Member]
Advertising costs [Line Items]
Deferred advertising costs amortization period	6 months
Direct Checks [Member]
Advertising costs [Line Items]
Percentage of deferred advertising costs expensed within six months	87.00%