Bank segment - Credit risk profile - summary (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Credit risk profile based on nonaccrual loans
Nonaccrual loans	$ 52,616	$ 46,035
Accruing loans 90 days or more past due	393	0
Total troubled debt restructuring loans not included above	25,740	22,246
Residential 1-4 family
Credit risk profile based on nonaccrual loans
Nonaccrual loans	20,929	20,554
Accruing loans 90 days or more past due	0	0
Total troubled debt restructuring loans not included above	13,308	13,962
Commercial real estate
Credit risk profile based on nonaccrual loans
Nonaccrual loans	3,762	1,188
Accruing loans 90 days or more past due	0	0
Total troubled debt restructuring loans not included above	0	0
Home equity line of credit
Credit risk profile based on nonaccrual loans
Nonaccrual loans	2,404	2,254
Accruing loans 90 days or more past due	0	0
Total troubled debt restructuring loans not included above	4,501	2,467
Residential land
Credit risk profile based on nonaccrual loans
Nonaccrual loans	776	970
Accruing loans 90 days or more past due	393	0
Total troubled debt restructuring loans not included above	3,258	4,713
Commercial construction
Credit risk profile based on nonaccrual loans
Nonaccrual loans	0	0
Accruing loans 90 days or more past due	0	0
Total troubled debt restructuring loans not included above	0	0
Residential construction
Credit risk profile based on nonaccrual loans
Nonaccrual loans	0	0
Accruing loans 90 days or more past due	0	0
Total troubled debt restructuring loans not included above	0	0
Commercial loans
Credit risk profile based on nonaccrual loans
Nonaccrual loans	23,588	20,174
Accruing loans 90 days or more past due	0	0
Total troubled debt restructuring loans not included above	4,673	1,104
Consumer loans
Credit risk profile based on nonaccrual loans
Nonaccrual loans	1,157	895
Accruing loans 90 days or more past due	0	0
Total troubled debt restructuring loans not included above	$ 0	$ 0