Bank segment - Troubled debt restructuring that subsequently defaulted (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) contract	Jun. 30, 2016 USD ($) contract	Jun. 30, 2017 USD ($) contract	Jun. 30, 2016 USD ($) contract
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	1	1	2	2
Recorded investment | $	$ 222	$ 26	$ 523	$ 514
Residential 1-4 family
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	1	0	2	1
Recorded investment | $	$ 222	$ 0	$ 523	$ 488
Commercial real estate
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	0	0
Recorded investment | $	$ 0	$ 0	$ 0	$ 0
Home equity line of credit
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	0	0
Recorded investment | $	$ 0	$ 0	$ 0	$ 0
Residential land
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	0	0
Recorded investment | $	$ 0	$ 0	$ 0	$ 0
Commercial construction
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	0	0
Recorded investment | $	$ 0	$ 0	$ 0	$ 0
Residential construction
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	0	0
Recorded investment | $	$ 0	$ 0	$ 0	$ 0
Commercial loans
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	1	0	1
Recorded investment | $	$ 0	$ 26	$ 0	$ 26
Consumer loans
Financing Receivable, Modifications [Line Items]
Number of contracts (in contracts) | contract	0	0	0	0
Recorded investment | $	$ 0	$ 0	$ 0	$ 0