Bank segment - Credit risk profile - payment activity and assigned grades (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Credit risk profile by internally assigned grade for loans
June 30, 2020	$ 771,600
December 31, 2019	695,446
December 31, 2018	488,691
December 31, 2017	407,684
December 31, 2016	408,551
Prior	1,391,212
Revolving	1,221,590
Converted to term loans	66,028
Total	5,450,802	$ 5,120,664
Real estate
Credit risk profile by internally assigned grade for loans
Total	4,160,943	4,192,069
Real estate | Residential 1-4 family
Credit risk profile by internally assigned grade for loans
June 30, 2020	176,536
December 31, 2019	272,951
December 31, 2018	165,584
December 31, 2017	258,464
December 31, 2016	215,920
Prior	1,033,771
Revolving	0
Converted to term loans	0
Total	2,123,226	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	1,030,145
Converted to term loans	35,119
Total	1,065,264	1,092,125
Conversion of debt	8,700
Real estate | Residential land
Credit risk profile by internally assigned grade for loans
June 30, 2020	2,095
December 31, 2019	4,975
December 31, 2018	2,024
December 31, 2017	2,041
December 31, 2016	22
Prior	2,067
Revolving	0
Converted to term loans	0
Total	13,224	14,704
Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	2,725
December 31, 2019	5,034
December 31, 2018	974
December 31, 2017	2,026
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	10,759	11,670
Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
June 30, 2020	99,566
December 31, 2019	119,500
December 31, 2018	134,836
December 31, 2017	65,395
December 31, 2016	129,333
Prior	289,717
Revolving	17,219
Converted to term loans	0
Total	855,566	824,830
Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	7,752
December 31, 2019	13,458
December 31, 2018	29,873
December 31, 2017	18,000
December 31, 2016	7,472
Prior	2,289
Revolving	14,060
Converted to term loans	0
Total	92,904	70,605
Consumer
Credit risk profile by internally assigned grade for loans
June 30, 2020	25,469
December 31, 2019	90,480
December 31, 2018	56,187
December 31, 2017	15,772
December 31, 2016	1,717
Prior	505
Revolving	22,563
Converted to term loans	3,337
Total	216,030	257,921
Conversion of debt	1,400
Commercial
Credit risk profile by internally assigned grade for loans
June 30, 2020	457,457
December 31, 2019	189,048
December 31, 2018	99,213
December 31, 2017	45,986
December 31, 2016	54,087
Prior	62,863
Revolving	137,603
Converted to term loans	27,572
Total	1,073,829	$ 670,674
Conversion of debt	13,700
Pass | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
June 30, 2020	89,882
December 31, 2019	77,350
December 31, 2018	78,115
December 31, 2017	29,390
December 31, 2016	56,246
Prior	172,941
Revolving	17,219
Converted to term loans	0
Total	521,143
Pass | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	6,933
December 31, 2019	13,458
December 31, 2018	29,873
December 31, 2017	0
December 31, 2016	7,472
Prior	0
Revolving	14,060
Converted to term loans	0
Total	71,796
Pass | Commercial
Credit risk profile by internally assigned grade for loans
June 30, 2020	450,699
December 31, 2019	154,672
December 31, 2018	94,309
December 31, 2017	33,771
December 31, 2016	13,876
Prior	38,911
Revolving	92,475
Converted to term loans	14,868
Total	893,581
Special Mention | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
June 30, 2020	9,684
December 31, 2019	41,662
December 31, 2018	54,791
December 31, 2017	35,400
December 31, 2016	69,418
Prior	60,098
Revolving	0
Converted to term loans	0
Total	271,053
Special Mention | Real estate | Commercial construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	819
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	18,819
Special Mention | Commercial
Credit risk profile by internally assigned grade for loans
June 30, 2020	6,593
December 31, 2019	29,695
December 31, 2018	4,759
December 31, 2017	10,578
December 31, 2016	38,970
Prior	20,813
Revolving	44,521
Converted to term loans	11,222
Total	167,151
Substandard | Real estate | Commercial real estate
Credit risk profile by internally assigned grade for loans
June 30, 2020	0
December 31, 2019	488
December 31, 2018	1,930
December 31, 2017	605
December 31, 2016	3,669
Prior	56,678
Revolving	0
Converted to term loans	0
Total	63,370
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	2,289
Revolving	0
Converted to term loans	0
Total	2,289
Substandard | Commercial
Credit risk profile by internally assigned grade for loans
June 30, 2020	165
December 31, 2019	4,681
December 31, 2018	145
December 31, 2017	1,637
December 31, 2016	1,241
Prior	3,139
Revolving	607
Converted to term loans	1,482
Total	13,097
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	176,536
December 31, 2019	272,951
December 31, 2018	165,584
December 31, 2017	258,111
December 31, 2016	215,920
Prior	1,029,434
Revolving	0
Converted to term loans	0
Total	2,118,536
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	1,027,589
Converted to term loans	33,797
Total	1,061,386
Current | Real estate | Residential land
Credit risk profile by internally assigned grade for loans
June 30, 2020	2,095
December 31, 2019	4,975
December 31, 2018	2,024
December 31, 2017	2,041
December 31, 2016	22
Prior	2,067
Revolving	0
Converted to term loans	0
Total	13,224
Current | Real estate | Residential construction
Credit risk profile by internally assigned grade for loans
June 30, 2020	2,725
December 31, 2019	5,034
December 31, 2018	974
December 31, 2017	2,026
December 31, 2016	0
Prior	0
Revolving	0
Converted to term loans	0
Total	10,759
Current | Consumer
Credit risk profile by internally assigned grade for loans
June 30, 2020	25,186
December 31, 2019	87,908
December 31, 2018	53,640
December 31, 2017	14,851
December 31, 2016	1,602
Prior	505
Revolving	21,691
Converted to term loans	3,062
Total	208,445
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	2,192
Revolving	0
Converted to term loans	0
Total	2,192
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	790
Converted to term loans	312
Total	1,102
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	0
Revolving	0
Converted to term loans	0
Total	0
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	105
December 31, 2019	573
December 31, 2018	583
December 31, 2017	229
December 31, 2016	18
Prior	0
Revolving	200
Converted to term loans	44
Total	1,752
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	606
Revolving	0
Converted to term loans	0
Total	606
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	408
Converted to term loans	175
Total	583
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	83
December 31, 2019	741
December 31, 2018	792
December 31, 2017	209
December 31, 2016	24
Prior	0
Revolving	248
Converted to term loans	67
Total	2,164
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	1,539
Revolving	0
Converted to term loans	0
Total	1,892
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	1,358
Converted to term loans	835
Total	2,193
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	95
December 31, 2019	1,258
December 31, 2018	1,172
December 31, 2017	483
December 31, 2016	73
Prior	0
Revolving	424
Converted to term loans	164
Total	$ 3,669