Bank segment - Troubled debt restructuring that subsequently defaulted (Details) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($) contract	Sep. 30, 2018 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	2
Recorded investment | $	$ 0	$ 372
Residential 1-4 family
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Home equity line of credit
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	1
Recorded investment | $	$ 0	$ 81
Residential land
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Residential construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Commercial loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	1
Recorded investment | $	$ 0	$ 291
Consumer loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0