Basis of presentation and summary of significant accounting policies (Schedule of Premises and Equipment) (Details)	12 Months Ended
	Dec. 31, 2016
Land Improvements | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, useful life	3 years
Land Improvements | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, useful life	15 years
Building | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, useful life	5 years
Building | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, useful life	39 years
Computer | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, useful life	3 years
Computer | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, useful life	5 years
Furniture, Fixtures, and Other Equipment | Minimum
Property, Plant and Equipment [Line Items]
Premises and equipment, useful life	3 years
Furniture, Fixtures, and Other Equipment | Maximum
Property, Plant and Equipment [Line Items]
Premises and equipment, useful life	15 years