Bank segment - Credit risk profile - payment activity and assigned grades (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Credit risk profile by internally assigned grade for loans
June 30, 2020	$ 1,134,977
December 31, 2019	632,640
December 31, 2018	446,401
December 31, 2017	372,750
December 31, 2016	389,536
Prior	1,288,936
Revolving	1,164,951
Converted to term loans	63,919
Total	5,494,110	$ 5,120,664
Real estate
Credit risk profile by internally assigned grade for loans
Total	4,261,537	4,192,069
Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
June 30, 2020	425,930
December 31, 2019	242,811
December 31, 2018	138,155
December 31, 2017	234,297
December 31, 2016	201,532
Prior	952,368
Revolving	0
Converted to term loans	0
Total	2,195,093	2,178,135
Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	993,063
Converted to term loans	34,948
Total	1,028,011	1,092,125
Conversion of debt	10,000
Real estate | Residential land
Credit risk profile by internally assigned grade for loans
June 30, 2020	4,606
December 31, 2019	4,433
December 31, 2018	1,598
December 31, 2017	1,600
December 31, 2016	22
Prior	2,051
Revolving	0
Converted to term loans	0
Total	14,310	14,704
Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	4,368
December 31, 2019	4,897
December 31, 2018	386
December 31, 2017	630
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	10,281	11,670
Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
June 30, 2020	170,764
December 31, 2019	115,159
December 31, 2018	133,115
December 31, 2017	64,502
December 31, 2016	128,705
Prior	277,667
Revolving	11,000
Converted to term loans	0
Total	900,912	824,830
Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	12,754
December 31, 2019	21,322
December 31, 2018	30,655
December 31, 2017	18,000
December 31, 2016	5,999
Prior	0
Revolving	24,200
Converted to term loans	0
Total	112,930	70,605
Consumer
Credit risk profile by internally assigned grade for loans
June 30, 2020	26,175
December 31, 2019	79,659
December 31, 2018	47,293
December 31, 2017	11,463
December 31, 2016	800
Prior	423
Revolving	20,802
Converted to term loans	3,523
Total	190,138	257,921
Conversion of debt	2,000
Commercial
Credit risk profile by internally assigned grade for loans
June 30, 2020	490,380
December 31, 2019	164,359
December 31, 2018	95,199
December 31, 2017	42,258
December 31, 2016	52,478
Prior	56,427
Revolving	115,886
Converted to term loans	25,448
Total	1,042,435	$ 670,674
Conversion of debt	13,800
Pass | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
June 30, 2020	161,130
December 31, 2019	73,086
December 31, 2018	63,082
December 31, 2017	28,685
December 31, 2016	55,742
Prior	154,297
Revolving	11,000
Converted to term loans	0
Total	547,022
Pass | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	11,122
December 31, 2019	21,322
December 31, 2018	30,655
December 31, 2017	0
December 31, 2016	5,999
Prior	0
Revolving	24,200
Converted to term loans	0
Total	93,298
Pass | Commercial
Credit risk profile by internally assigned grade for loans
June 30, 2020	454,219
December 31, 2019	131,481
December 31, 2018	91,147
December 31, 2017	30,680
December 31, 2016	13,067
Prior	37,580
Revolving	76,449
Converted to term loans	13,397
Total	848,020
Special Mention | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
June 30, 2020	9,634
December 31, 2019	38,908
December 31, 2018	65,840
December 31, 2017	33,921
December 31, 2016	68,502
Prior	65,431
Revolving	0
Converted to term loans	0
Total	282,236
Special Mention | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	1,632
December 31, 2019	0
December 31, 2018	0
December 31, 2017	18,000
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	19,632
Special Mention | Commercial
Credit risk profile by internally assigned grade for loans
June 30, 2020	36,029
December 31, 2019	23,458
December 31, 2018	3,681
December 31, 2017	7,176
December 31, 2016	30,864
Prior	15,105
Revolving	32,494
Converted to term loans	11,221
Total	160,028
Substandard | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	3,165
December 31, 2018	4,193
December 31, 2017	1,896
December 31, 2016	4,461
Prior	57,939
Revolving	0
Converted to term loans	0
Total	71,654
Substandard | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	0
Substandard | Commercial
Credit risk profile by internally assigned grade for loans
June 30, 2020	132
December 31, 2019	9,420
December 31, 2018	371
December 31, 2017	4,402
December 31, 2016	8,547
Prior	3,742
Revolving	6,943
Converted to term loans	830
Total	34,387
Doubtful | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	0
Doubtful | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	0
Doubtful | Commercial
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	0
Current | Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
June 30, 2020	425,930
December 31, 2019	242,811
December 31, 2018	138,155
December 31, 2017	233,944
December 31, 2016	201,532
Prior	947,343
Revolving	0
Converted to term loans	0
Total	2,189,715
Current | Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	991,199
Converted to term loans	33,800
Total	1,024,999
Current | Real estate | Residential land
Credit risk profile by internally assigned grade for loans
June 30, 2020	4,606
December 31, 2019	4,433
December 31, 2018	1,598
December 31, 2017	1,600
December 31, 2016	22
Prior	1,751
Revolving	0
Converted to term loans	0
Total	14,010
Current | Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	4,368
December 31, 2019	4,897
December 31, 2018	386
December 31, 2017	630
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	10,281
Current | Consumer
Credit risk profile by internally assigned grade for loans
June 30, 2020	25,661
December 31, 2019	77,454
December 31, 2018	45,485
December 31, 2017	10,916
December 31, 2016	764
Prior	423
Revolving	19,906
Converted to term loans	3,221
Total	183,830
30-59 days past due | Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	2,461
Revolving	0
Converted to term loans	0
Total	2,461
30-59 days past due | Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	419
Converted to term loans	349
Total	768
30-59 days past due | Real estate | Residential land
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	300
Revolving	0
Converted to term loans	0
Total	300
30-59 days past due | Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	0
30-59 days past due | Consumer
Credit risk profile by internally assigned grade for loans
June 30, 2020	387
December 31, 2019	981
December 31, 2018	723
December 31, 2017	239
December 31, 2016	13
Prior	0
Revolving	467
Converted to term loans	131
Total	2,941
60-89 days past due | Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	1,028
Revolving	0
Converted to term loans	0
Total	1,028
60-89 days past due | Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	158
Converted to term loans	0
Total	158
60-89 days past due | Real estate | Residential land
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	0
60-89 days past due | Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	0
60-89 days past due | Consumer
Credit risk profile by internally assigned grade for loans
June 30, 2020	95
December 31, 2019	717
December 31, 2018	674
December 31, 2017	152
December 31, 2016	5
Prior	0
Revolving	70
Converted to term loans	87
Total	1,800
Greater than 89 days past due | Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	353
December 31, 2016	0
Prior	1,536
Revolving	0
Converted to term loans	0
Total	1,889
Greater than 89 days past due | Real estate | Home equity line of credit
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	1,287
Converted to term loans	799
Total	2,086
Greater than 89 days past due | Real estate | Residential land
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	0
Greater than 89 days past due | Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	0
December 31, 2018	0
December 31, 2017	0
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	0
Greater than 89 days past due | Consumer
Credit risk profile by internally assigned grade for loans
June 30, 2020	32
December 31, 2019	507
December 31, 2018	411
December 31, 2017	156
December 31, 2016	18
Prior	0
Revolving	359
Converted to term loans	84
Total	$ 1,567