Bank segment - Credit risk profile - payment activity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Credit risk profile based on payment activity for loans
Total past due	$ 20,897	$ 25,969
Current	5,062,759	4,817,665
Total financing receivables	5,083,656	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	7,834	10,440
60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	4,718	6,901
Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	8,345	8,628
Residential 1-4 family
Credit risk profile based on payment activity for loans
Total past due	5,421	8,869
Current	2,178,467	2,134,528
Total financing receivables	2,183,888	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	2,162	3,757
Residential 1-4 family | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	807	2,773
Residential 1-4 family | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	2,452	2,339
Commercial real estate
Credit risk profile based on payment activity for loans
Total past due	347	0
Current	810,624	748,398
Total financing receivables	810,971	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	347	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	3,677	4,540
Current	1,075,585	973,697
Total financing receivables	1,079,262	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	736	1,139
Home equity line of credit | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	814	681
Home equity line of credit | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	2,127	2,720
Residential land
Credit risk profile based on payment activity for loans
Total past due	25	328
Current	15,070	12,810
Total financing receivables	15,095	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	0	9
Residential land | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	0	0
Residential land | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	25	319
Commercial construction
Credit risk profile based on payment activity for loans
Total past due	0	0
Current	76,382	92,264
Total financing receivables	76,382	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	10,104	14,307
Total financing receivables	10,104	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	1,813	1,144
Current	636,400	586,747
Total financing receivables	638,213	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	359	315
Commercial loans | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	174	281
Commercial loans | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	1,280	548
Consumer loans
Credit risk profile based on payment activity for loans
Total past due	9,614	11,088
Current	260,127	254,914
Total financing receivables	269,741	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	4,230	5,220
Consumer loans | 60-89 days past due
Credit risk profile based on payment activity for loans
Total past due	2,923	3,166
Consumer loans | Greater than 90 days
Credit risk profile based on payment activity for loans
Total past due	$ 2,461	$ 2,702