Bank segment - Credit risk profile - payment activity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Credit risk profile based on payment activity for loans
Financing receivable, past due	$ 17,131	$ 19,751
Financing receivable, current	5,476,979	5,100,913
Total	5,494,110	5,120,664
Recorded Investment greater than 90 days and accruing	0	0
Real estate
Credit risk profile based on payment activity for loans
Total	4,261,537	4,192,069
Real estate | Residential 1-4 family
Credit risk profile based on payment activity for loans
Financing receivable, past due	5,378	4,686
Financing receivable, current	2,189,715	2,173,449
Total	2,195,093	2,178,135
Recorded Investment greater than 90 days and accruing	0	0
Real estate | Commercial real estate
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
Financing receivable, current	900,912	824,830
Total	900,912	824,830
Recorded Investment greater than 90 days and accruing	0	0
Real estate | Home equity line of credit
Credit risk profile based on payment activity for loans
Financing receivable, past due	3,012	2,930
Financing receivable, current	1,024,999	1,089,195
Total	1,028,011	1,092,125
Recorded Investment greater than 90 days and accruing	0	0
Real estate | Residential land
Credit risk profile based on payment activity for loans
Financing receivable, past due	300	25
Financing receivable, current	14,010	14,679
Total	14,310	14,704
Recorded Investment greater than 90 days and accruing	0	0
Real estate | Commercial construction
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
Financing receivable, current	112,930	70,605
Total	112,930	70,605
Recorded Investment greater than 90 days and accruing	0	0
Real estate | Residential construction
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
Financing receivable, current	10,281	11,670
Total	10,281	11,670
Recorded Investment greater than 90 days and accruing	0	0
Commercial
Credit risk profile based on payment activity for loans
Financing receivable, past due	2,133	1,560
Financing receivable, current	1,040,302	669,114
Total	1,042,435	670,674
Recorded Investment greater than 90 days and accruing	0	0
Consumer
Credit risk profile based on payment activity for loans
Financing receivable, past due	6,308	10,550
Financing receivable, current	183,830	247,371
Total	190,138	257,921
Recorded Investment greater than 90 days and accruing	0	0
30-59 days past due
Credit risk profile based on payment activity for loans
Financing receivable, past due	8,172	8,864
30-59 days past due | Real estate | Residential 1-4 family
Credit risk profile based on payment activity for loans
Financing receivable, past due	2,461	2,588
Total	2,461
30-59 days past due | Real estate | Commercial real estate
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
30-59 days past due | Real estate | Home equity line of credit
Credit risk profile based on payment activity for loans
Financing receivable, past due	768	813
Total	768
30-59 days past due | Real estate | Residential land
Credit risk profile based on payment activity for loans
Financing receivable, past due	300	0
Total	300
30-59 days past due | Real estate | Commercial construction
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
30-59 days past due | Real estate | Residential construction
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
Total	0
30-59 days past due | Commercial
Credit risk profile based on payment activity for loans
Financing receivable, past due	1,702	1,077
30-59 days past due | Consumer
Credit risk profile based on payment activity for loans
Financing receivable, past due	2,941	4,386
Total	2,941
60-89 days past due
Credit risk profile based on payment activity for loans
Financing receivable, past due	3,312	3,858
60-89 days past due | Real estate | Residential 1-4 family
Credit risk profile based on payment activity for loans
Financing receivable, past due	1,028	290
Total	1,028
60-89 days past due | Real estate | Commercial real estate
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
60-89 days past due | Real estate | Home equity line of credit
Credit risk profile based on payment activity for loans
Financing receivable, past due	158	0
Total	158
60-89 days past due | Real estate | Residential land
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
Total	0
60-89 days past due | Real estate | Commercial construction
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
60-89 days past due | Real estate | Residential construction
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
Total	0
60-89 days past due | Commercial
Credit risk profile based on payment activity for loans
Financing receivable, past due	326	311
60-89 days past due | Consumer
Credit risk profile based on payment activity for loans
Financing receivable, past due	1,800	3,257
Total	1,800
90 days or more past due
Credit risk profile based on payment activity for loans
Financing receivable, past due	5,647	7,029
90 days or more past due | Real estate | Residential 1-4 family
Credit risk profile based on payment activity for loans
Financing receivable, past due	1,889	1,808
Total	1,889
90 days or more past due | Real estate | Commercial real estate
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
90 days or more past due | Real estate | Home equity line of credit
Credit risk profile based on payment activity for loans
Financing receivable, past due	2,086	2,117
Total	2,086
90 days or more past due | Real estate | Residential land
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	25
Total	0
90 days or more past due | Real estate | Commercial construction
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
90 days or more past due | Real estate | Residential construction
Credit risk profile based on payment activity for loans
Financing receivable, past due	0	0
Total	0
90 days or more past due | Commercial
Credit risk profile based on payment activity for loans
Financing receivable, past due	105	172
90 days or more past due | Consumer
Credit risk profile based on payment activity for loans
Financing receivable, past due	1,567	$ 2,907
Total	$ 1,567