Loans and allowance for credit losses - Amortized Cost Basis by Origination Year (Details) $ in Thousands	Jun. 30, 2020 USD ($)
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	$ 656,419
2019	885,291
2018	676,583
2017	496,947
2016	429,551
Prior	736,990
Revolving Loans Amortized Cost Basis	945,242
Total	4,827,023
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	342,021
2019	182,079
2018	107,437
2017	48,901
2016	40,006
Prior	39,559
Revolving Loans Amortized Cost Basis	529,643
Total	1,289,646
Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	62,393
2019	172,093
2018	74,821
2017	42,793
2016	33,530
Prior	77,161
Revolving Loans Amortized Cost Basis	90,828
Total	553,619
Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	100,879
2019	174,015
2018	139,863
2017	95,478
2016	68,007
Prior	163,694
Revolving Loans Amortized Cost Basis	0
Total	741,936
Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	56
2019	0
2018	0
2017	0
2016	284
Prior	3,374
Revolving Loans Amortized Cost Basis	233,260
Total	236,974
Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	20,796
2019	14,346
2018	6,758
2017	42,196
2016	2,965
Prior	28,088
Revolving Loans Amortized Cost Basis	0
Total	115,149
Residential real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	36,153
2019	142,060
2018	213,772
2017	137,765
2016	168,950
Prior	199,481
Revolving Loans Amortized Cost Basis	25,011
Total	923,192
Commercial real estate:
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	50,660
2019	139,317
2018	86,145
2017	97,742
2016	68,447
Prior	183,544
Revolving Loans Amortized Cost Basis	57,390
Total	683,245
Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	43,461
2019	61,381
2018	47,787
2017	32,072
2016	47,362
Prior	42,089
Revolving Loans Amortized Cost Basis	9,110
Total	283,262
Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	649,453
2019	856,233
2018	620,148
2017	438,051
2016	402,040
Prior	645,421
Revolving Loans Amortized Cost Basis	883,818
Total	4,495,164
Pass | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	338,964
2019	168,783
2018	69,250
2017	41,722
2016	32,820
Prior	31,449
Revolving Loans Amortized Cost Basis	481,897
Total	1,164,885
Pass | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	62,335
2019	170,746
2018	74,183
2017	32,656
2016	32,790
Prior	71,149
Revolving Loans Amortized Cost Basis	90,620
Total	534,479
Pass | Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	99,613
2019	172,190
2018	137,308
2017	89,665
2016	62,505
Prior	142,668
Revolving Loans Amortized Cost Basis	0
Total	703,949
Pass | Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	56
2019	0
2018	0
2017	0
2016	284
Prior	3,297
Revolving Loans Amortized Cost Basis	230,334
Total	233,971
Pass | Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	20,796
2019	14,346
2018	6,758
2017	42,196
2016	2,965
Prior	28,030
Revolving Loans Amortized Cost Basis	0
Total	115,091
Pass | Residential real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	34,657
2019	139,867
2018	202,792
2017	132,792
2016	164,798
Prior	175,966
Revolving Loans Amortized Cost Basis	24,834
Total	875,706
Pass | Commercial real estate:
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	49,663
2019	129,755
2018	84,301
2017	69,678
2016	62,755
Prior	161,851
Revolving Loans Amortized Cost Basis	48,023
Total	606,026
Pass | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	43,369
2019	60,546
2018	45,556
2017	29,342
2016	43,123
Prior	31,011
Revolving Loans Amortized Cost Basis	8,110
Total	261,057
Watch
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	6,329
2019	21,812
2018	47,968
2017	46,786
2016	22,902
Prior	48,721
Revolving Loans Amortized Cost Basis	48,925
Total	243,443
Watch | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	2,791
2019	10,761
2018	33,603
2017	3,928
2016	5,772
Prior	4,414
Revolving Loans Amortized Cost Basis	39,740
Total	101,009
Watch | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	58
2019	10
2018	229
2017	10,126
2016	740
Prior	2,807
Revolving Loans Amortized Cost Basis	0
Total	13,970
Watch | Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	913
2019	603
2018	608
2017	2,139
2016	3,537
Prior	12,938
Revolving Loans Amortized Cost Basis	0
Total	20,738
Watch | Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	788
Total	788
Watch | Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	58
Revolving Loans Amortized Cost Basis	0
Total	58
Watch | Residential real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	1,496
2019	2,193
2018	10,707
2017	4,973
2016	3,769
Prior	5,090
Revolving Loans Amortized Cost Basis	94
Total	28,322
Watch | Commercial real estate:
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	997
2019	7,758
2018	1,530
2017	24,105
2016	5,634
Prior	14,847
Revolving Loans Amortized Cost Basis	7,716
Total	62,587
Watch | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	74
2019	487
2018	1,291
2017	1,515
2016	3,450
Prior	8,567
Revolving Loans Amortized Cost Basis	587
Total	15,971
Substandard
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	621
2019	6,826
2018	8,067
2017	11,586
2016	4,228
Prior	41,979
Revolving Loans Amortized Cost Basis	11,853
Total	85,160
Substandard | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	250
2019	2,535
2018	4,584
2017	3,251
2016	1,414
Prior	3,696
Revolving Loans Amortized Cost Basis	7,806
Total	23,536
Substandard | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	1,170
2018	409
2017	11
2016	0
Prior	3,205
Revolving Loans Amortized Cost Basis	208
Total	5,003
Substandard | Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	353
2019	1,222
2018	1,891
2017	3,674
2016	1,640
Prior	7,664
Revolving Loans Amortized Cost Basis	0
Total	16,444
Substandard | Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	77
Revolving Loans Amortized Cost Basis	1,692
Total	1,769
Substandard | Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total	0
Substandard | Residential real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	273
2017	0
2016	383
Prior	18,425
Revolving Loans Amortized Cost Basis	83
Total	19,164
Substandard | Commercial real estate:
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	1,804
2018	314
2017	3,959
2016	58
Prior	6,846
Revolving Loans Amortized Cost Basis	1,651
Total	14,632
Substandard | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	18
2019	95
2018	596
2017	691
2016	733
Prior	2,066
Revolving Loans Amortized Cost Basis	413
Total	4,612
Doubtful
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	16
2019	420
2018	400
2017	524
2016	381
Prior	869
Revolving Loans Amortized Cost Basis	646
Total	3,256
Doubtful | Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	16
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	200
Total	216
Doubtful | Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	167
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total	167
Doubtful | Residential real estate: | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	56
2017	0
2016	325
Prior	424
Revolving Loans Amortized Cost Basis	0
Total	805
Doubtful | Residential real estate: | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	446
Total	446
Doubtful | Residential real estate: | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total	0
Doubtful | Residential real estate: | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total	0
Doubtful | Commercial real estate:
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	0
2018	0
2017	0
2016	0
Prior	0
Revolving Loans Amortized Cost Basis	0
Total	0
Doubtful | Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
2020	0
2019	253
2018	344
2017	524
2016	56
Prior	445
Revolving Loans Amortized Cost Basis	0
Total	$ 1,622