Bank segment - Troubled debt restructuring that subsequently defaulted (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) contract	Mar. 31, 2017 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	2	1
Recorded investment | $	$ 135	$ 301
Residential 1-4 family
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	1	1
Recorded investment | $	$ 49	$ 301
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Home equity line of credit
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	1	0
Recorded investment | $	$ 86	$ 0
Residential land
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Commercial construction
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Residential construction
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Commercial loans
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
Consumer loans
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0