Bank segment - Credit risk profile - payment activity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Credit risk profile based on payment activity for loans
Total past due	$ 30,462	$ 25,969
Current	4,827,808	4,817,665
Total financing receivables	4,858,270	4,843,634
Recorded Investment greater than 90 days and accruing	0	0
30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	14,252	10,440
60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	6,814	6,901
Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	9,396	8,628
Residential 1-4 family
Credit risk profile based on payment activity for loans
Total past due	9,445	8,869
Current	2,150,441	2,134,528
Total financing receivables	2,159,886	2,143,397
Recorded Investment greater than 90 days and accruing	0	0
Residential 1-4 family | 30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	2,625	3,757
Residential 1-4 family | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	2,954	2,773
Residential 1-4 family | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	3,866	2,339
Commercial real estate
Credit risk profile based on payment activity for loans
Total past due	2,225	0
Current	735,264	748,398
Total financing receivables	737,489	748,398
Recorded Investment greater than 90 days and accruing	0	0
Commercial real estate | 30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	2,225	0
Commercial real estate | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	0	0
Commercial real estate | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	0	0
Home equity line of credit
Credit risk profile based on payment activity for loans
Total past due	4,221	4,540
Current	991,403	973,697
Total financing receivables	995,624	978,237
Recorded Investment greater than 90 days and accruing	0	0
Home equity line of credit | 30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	1,244	1,139
Home equity line of credit | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	251	681
Home equity line of credit | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	2,726	2,720
Residential land
Credit risk profile based on payment activity for loans
Total past due	1,315	328
Current	11,626	12,810
Total financing receivables	12,941	13,138
Recorded Investment greater than 90 days and accruing	0	0
Residential land | 30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	818	9
Residential land | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	488	0
Residential land | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	9	319
Commercial construction
Credit risk profile based on payment activity for loans
Total past due	0	0
Current	98,734	92,264
Total financing receivables	98,734	92,264
Recorded Investment greater than 90 days and accruing	0	0
Commercial construction | 30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	0	0
Commercial construction | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	0	0
Commercial construction | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	0	0
Residential construction
Credit risk profile based on payment activity for loans
Total past due	0	0
Current	10,924	14,307
Total financing receivables	10,924	14,307
Recorded Investment greater than 90 days and accruing	0	0
Residential construction | 30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	0	0
Residential construction | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	0	0
Residential construction | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	0	0
Commercial loans
Credit risk profile based on payment activity for loans
Total past due	4,074	1,144
Current	572,161	586,747
Total financing receivables	576,235	587,891
Recorded Investment greater than 90 days and accruing	0	0
Commercial loans | 30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	3,167	315
Commercial loans | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	570	281
Commercial loans | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	337	548
Consumer loans
Credit risk profile based on payment activity for loans
Total past due	9,182	11,088
Current	257,255	254,914
Total financing receivables	266,437	266,002
Recorded Investment greater than 90 days and accruing	0	0
Consumer loans | 30-59 days past due
Credit risk profile based on payment activity for loans
Total past due	4,173	5,220
Consumer loans | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	2,551	3,166
Consumer loans | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	$ 2,458	$ 2,702