Bank segment - Troubled debt restructuring that subsequently defaulted (Details) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018 USD ($) contract	Jun. 30, 2018 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	2	3
Recorded investment | $	$ 391	$ 472
Residential 1-4 family
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0
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	2
Recorded investment | $	$ 100	$ 181
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	1	1
Recorded investment | $	$ 291	$ 291
Consumer loans
Financing Receivable, Modifications [Line Items]
Number of contracts | contract	0	0
Recorded investment | $	$ 0	$ 0