Loans and allowance for credit losses - Credit Quality of Loan Portfolio by Year of Origination (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	$ 402,808	$ 1,517,481
Before Current Fiscal Year	1,373,014	1,246,239
Two Years before Current Fiscal Year	1,124,786	853,371
Three Years before Current Fiscal Year	755,056	696,494
Four Years before Current Fiscal Year	559,143	648,821
Five Years before Current Fiscal Year	1,630,631	900,082
Revolving Loans Amortized Cost Basis	1,201,904	1,220,471
Loans	7,047,342	7,082,959
Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	402,377	1,513,764
Before Current Fiscal Year	1,368,913	1,235,808
Two Years before Current Fiscal Year	1,114,915	829,801
Three Years before Current Fiscal Year	708,372	679,220
Four Years before Current Fiscal Year	538,924	637,408
Five Years before Current Fiscal Year	1,575,399	855,663
Revolving Loans Amortized Cost Basis	1,181,854	1,199,072
Loans	6,890,754	6,950,736
Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	431	3,717
Before Current Fiscal Year	4,101	10,431
Two Years before Current Fiscal Year	9,871	23,570
Three Years before Current Fiscal Year	46,684	17,274
Four Years before Current Fiscal Year	20,219	11,413
Five Years before Current Fiscal Year	55,232	44,419
Revolving Loans Amortized Cost Basis	20,050	21,399
Loans	156,588	132,223
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	47,688	341,806
Before Current Fiscal Year	267,004	189,148
Two Years before Current Fiscal Year	179,603	82,337
Three Years before Current Fiscal Year	78,648	64,787
Four Years before Current Fiscal Year	52,930	45,070
Five Years before Current Fiscal Year	88,857	46,542
Revolving Loans Amortized Cost Basis	577,800	576,432
Loans	1,292,530	1,346,122
Commercial and industrial | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	47,458	339,305
Before Current Fiscal Year	264,285	186,460
Two Years before Current Fiscal Year	177,250	71,110
Three Years before Current Fiscal Year	67,564	60,362
Four Years before Current Fiscal Year	49,794	38,488
Five Years before Current Fiscal Year	80,524	45,265
Revolving Loans Amortized Cost Basis	568,385	565,786
Loans	1,255,260	1,306,776
Commercial and industrial | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	230	2,501
Before Current Fiscal Year	2,719	2,688
Two Years before Current Fiscal Year	2,353	11,227
Three Years before Current Fiscal Year	11,084	4,425
Four Years before Current Fiscal Year	3,136	6,582
Five Years before Current Fiscal Year	8,333	1,277
Revolving Loans Amortized Cost Basis	9,415	10,646
Loans	37,270	39,346
Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	87,958	462,757
Before Current Fiscal Year	446,596	393,683
Two Years before Current Fiscal Year	266,062	91,865
Three Years before Current Fiscal Year	54,111	54,304
Four Years before Current Fiscal Year	39,557	41,636
Five Years before Current Fiscal Year	123,701	65,971
Revolving Loans Amortized Cost Basis	102,600	112,004
Loans	1,120,585	1,222,220
Construction | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	87,958	462,184
Before Current Fiscal Year	446,596	391,928
Two Years before Current Fiscal Year	263,730	88,687
Three Years before Current Fiscal Year	50,161	54,163
Four Years before Current Fiscal Year	39,430	41,636
Five Years before Current Fiscal Year	120,595	62,903
Revolving Loans Amortized Cost Basis	102,600	112,004
Loans	1,111,070	1,213,505
Construction | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	573
Before Current Fiscal Year	0	1,755
Two Years before Current Fiscal Year	2,332	3,178
Three Years before Current Fiscal Year	3,950	141
Four Years before Current Fiscal Year	127	0
Five Years before Current Fiscal Year	3,106	3,068
Revolving Loans Amortized Cost Basis	0	0
Loans	9,515	8,715
Residential real estate | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	81,307	284,978
Before Current Fiscal Year	246,612	179,968
Two Years before Current Fiscal Year	151,965	169,514
Three Years before Current Fiscal Year	114,876	163,957
Four Years before Current Fiscal Year	93,078	115,537
Five Years before Current Fiscal Year	390,780	175,316
Revolving Loans Amortized Cost Basis	0	0
Loans	1,078,618	1,089,270
Residential real estate | 1-to-4 family mortgage | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	81,106	284,530
Before Current Fiscal Year	245,371	178,540
Two Years before Current Fiscal Year	150,194	165,708
Three Years before Current Fiscal Year	111,676	158,484
Four Years before Current Fiscal Year	87,975	111,915
Five Years before Current Fiscal Year	379,183	165,916
Revolving Loans Amortized Cost Basis	0	0
Loans	1,055,505	1,065,093
Residential real estate | 1-to-4 family mortgage | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	201	448
Before Current Fiscal Year	1,241	1,428
Two Years before Current Fiscal Year	1,771	3,806
Three Years before Current Fiscal Year	3,200	5,473
Four Years before Current Fiscal Year	5,103	3,622
Five Years before Current Fiscal Year	11,597	9,400
Revolving Loans Amortized Cost Basis	0	0
Loans	23,113	24,177
Residential real estate | Residential line of credit
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	0
Before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	0	0
Four Years before Current Fiscal Year	0	0
Five Years before Current Fiscal Year	0	0
Revolving Loans Amortized Cost Basis	394,510	408,211
Loans	394,510	408,211
Residential real estate | Residential line of credit | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	0
Before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	0	0
Four Years before Current Fiscal Year	0	0
Five Years before Current Fiscal Year	0	0
Revolving Loans Amortized Cost Basis	389,110	402,859
Loans	389,110	402,859
Residential real estate | Residential line of credit | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	0
Before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	0	0
Four Years before Current Fiscal Year	0	0
Five Years before Current Fiscal Year	0	0
Revolving Loans Amortized Cost Basis	5,400	5,352
Loans	5,400	5,352
Residential real estate | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	44,220	29,006
Before Current Fiscal Year	29,241	13,446
Two Years before Current Fiscal Year	76,432	11,843
Three Years before Current Fiscal Year	9,548	46,561
Four Years before Current Fiscal Year	39,549	28,330
Five Years before Current Fiscal Year	62,720	35,396
Revolving Loans Amortized Cost Basis	10,129	11,094
Loans	271,839	175,676
Residential real estate | Multi-family mortgage | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	44,220	29,006
Before Current Fiscal Year	29,241	13,446
Two Years before Current Fiscal Year	76,432	11,843
Three Years before Current Fiscal Year	9,548	46,561
Four Years before Current Fiscal Year	39,549	28,330
Five Years before Current Fiscal Year	62,665	35,339
Revolving Loans Amortized Cost Basis	10,129	11,094
Loans	271,784	175,619
Residential real estate | Multi-family mortgage | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	0
Before Current Fiscal Year	0	0
Two Years before Current Fiscal Year	0	0
Three Years before Current Fiscal Year	0	0
Four Years before Current Fiscal Year	0	0
Five Years before Current Fiscal Year	55	57
Revolving Loans Amortized Cost Basis	0	0
Loans	55	57
Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	32,420	141,915
Before Current Fiscal Year	141,912	182,641
Two Years before Current Fiscal Year	193,668	104,251
Three Years before Current Fiscal Year	100,661	116,906
Four Years before Current Fiscal Year	100,622	82,914
Five Years before Current Fiscal Year	303,860	237,800
Revolving Loans Amortized Cost Basis	63,330	58,414
Loans	936,473	924,841
Commercial real estate | Owner occupied | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	32,420	141,871
Before Current Fiscal Year	141,912	180,856
Two Years before Current Fiscal Year	192,702	101,828
Three Years before Current Fiscal Year	98,263	110,832
Four Years before Current Fiscal Year	94,382	82,640
Five Years before Current Fiscal Year	290,146	226,574
Revolving Loans Amortized Cost Basis	58,519	53,681
Loans	908,344	898,282
Commercial real estate | Owner occupied | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	44
Before Current Fiscal Year	0	1,785
Two Years before Current Fiscal Year	966	2,423
Three Years before Current Fiscal Year	2,398	6,074
Four Years before Current Fiscal Year	6,240	274
Five Years before Current Fiscal Year	13,714	11,226
Revolving Loans Amortized Cost Basis	4,811	4,733
Loans	28,129	26,559
Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	92,161	166,962
Before Current Fiscal Year	170,606	233,152
Two Years before Current Fiscal Year	207,744	350,814
Three Years before Current Fiscal Year	357,591	221,149
Four Years before Current Fiscal Year	207,765	290,370
Five Years before Current Fiscal Year	577,837	297,712
Revolving Loans Amortized Cost Basis	38,934	38,820
Loans	1,652,638	1,598,979
Commercial real estate | Non-owner occupied | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	92,161	166,962
Before Current Fiscal Year	170,606	230,942
Two Years before Current Fiscal Year	205,565	349,312
Three Years before Current Fiscal Year	332,674	221,149
Four Years before Current Fiscal Year	203,164	290,370
Five Years before Current Fiscal Year	562,311	280,629
Revolving Loans Amortized Cost Basis	38,934	38,820
Loans	1,605,415	1,578,184
Commercial real estate | Non-owner occupied | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	0
Before Current Fiscal Year	0	2,210
Two Years before Current Fiscal Year	2,179	1,502
Three Years before Current Fiscal Year	24,917	0
Four Years before Current Fiscal Year	4,601	0
Five Years before Current Fiscal Year	15,526	17,083
Revolving Loans Amortized Cost Basis	0	0
Loans	47,223	20,795
Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	17,054	90,057
Before Current Fiscal Year	71,043	54,201
Two Years before Current Fiscal Year	49,312	42,747
Three Years before Current Fiscal Year	39,621	28,830
Four Years before Current Fiscal Year	25,642	44,964
Five Years before Current Fiscal Year	82,876	41,345
Revolving Loans Amortized Cost Basis	14,601	15,496
Loans	300,149	317,640
Consumer and other | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	17,054	89,906
Before Current Fiscal Year	70,902	53,636
Two Years before Current Fiscal Year	49,042	41,313
Three Years before Current Fiscal Year	38,486	27,669
Four Years before Current Fiscal Year	24,630	44,029
Five Years before Current Fiscal Year	79,975	39,037
Revolving Loans Amortized Cost Basis	14,177	14,828
Loans	294,266	310,418
Consumer and other | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	151
Before Current Fiscal Year	141	565
Two Years before Current Fiscal Year	270	1,434
Three Years before Current Fiscal Year	1,135	1,161
Four Years before Current Fiscal Year	1,012	935
Five Years before Current Fiscal Year	2,901	2,308
Revolving Loans Amortized Cost Basis	424	668
Loans	$ 5,883	$ 7,222