Loans and allowance for credit losses - Credit Quality of Loan Portfolio by Year of Origination (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	$ 1,049,690	$ 1,517,481
Before Current Fiscal Year	1,196,905	1,246,239
Two Years before Current Fiscal Year	1,010,521	853,371
Three Years before Current Fiscal Year	726,171	696,494
Four Years before Current Fiscal Year	582,635	648,821
Five Years before Current Fiscal Year	1,366,409	900,082
Revolving Loans Amortized Cost Basis	1,266,623	1,220,471
Total	7,198,954	7,082,959
Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	1,048,846	1,510,393
Before Current Fiscal Year	1,192,101	1,228,017
Two Years before Current Fiscal Year	993,387	813,323
Three Years before Current Fiscal Year	672,356	660,160
Four Years before Current Fiscal Year	563,451	628,209
Five Years before Current Fiscal Year	1,294,350	836,930
Revolving Loans Amortized Cost Basis	1,230,153	1,171,352
Total	6,994,644	6,848,384
Special Mention
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	146	3,371
Before Current Fiscal Year	1,583	7,791
Two Years before Current Fiscal Year	2,973	16,478
Three Years before Current Fiscal Year	7,775	19,060
Four Years before Current Fiscal Year	3,470	9,199
Five Years before Current Fiscal Year	21,153	18,733
Revolving Loans Amortized Cost Basis	16,552	27,720
Total	53,652	102,352
Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	698	3,717
Before Current Fiscal Year	3,221	10,431
Two Years before Current Fiscal Year	14,161	23,570
Three Years before Current Fiscal Year	46,040	17,274
Four Years before Current Fiscal Year	15,714	11,413
Five Years before Current Fiscal Year	50,906	44,419
Revolving Loans Amortized Cost Basis	19,918	21,399
Total	150,658	132,223
Commercial and industrial
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	93,916	341,806
Before Current Fiscal Year	163,227	189,148
Two Years before Current Fiscal Year	165,099	82,337
Three Years before Current Fiscal Year	74,245	64,787
Four Years before Current Fiscal Year	52,402	45,070
Five Years before Current Fiscal Year	76,888	46,542
Revolving Loans Amortized Cost Basis	613,163	576,432
Total	1,238,940	1,346,122
Commercial and industrial | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	93,229	339,074
Before Current Fiscal Year	160,243	185,636
Two Years before Current Fiscal Year	162,002	70,549
Three Years before Current Fiscal Year	63,799	59,917
Four Years before Current Fiscal Year	48,206	37,573
Five Years before Current Fiscal Year	66,856	42,685
Revolving Loans Amortized Cost Basis	584,470	540,960
Total	1,178,805	1,276,394
Commercial and industrial | Special Mention
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	27	231
Before Current Fiscal Year	278	824
Two Years before Current Fiscal Year	423	561
Three Years before Current Fiscal Year	20	445
Four Years before Current Fiscal Year	468	915
Five Years before Current Fiscal Year	3,118	2,580
Revolving Loans Amortized Cost Basis	15,920	24,826
Total	20,254	30,382
Commercial and industrial | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	660	2,501
Before Current Fiscal Year	2,706	2,688
Two Years before Current Fiscal Year	2,674	11,227
Three Years before Current Fiscal Year	10,426	4,425
Four Years before Current Fiscal Year	3,728	6,582
Five Years before Current Fiscal Year	6,914	1,277
Revolving Loans Amortized Cost Basis	12,773	10,646
Total	39,881	39,346
Construction
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	261,384	462,757
Before Current Fiscal Year	393,596	393,683
Two Years before Current Fiscal Year	207,332	91,865
Three Years before Current Fiscal Year	52,939	54,304
Four Years before Current Fiscal Year	30,705	41,636
Five Years before Current Fiscal Year	88,260	65,971
Revolving Loans Amortized Cost Basis	110,949	112,004
Total	1,145,165	1,222,220
Construction | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	261,384	461,715
Before Current Fiscal Year	393,404	390,443
Two Years before Current Fiscal Year	205,133	86,490
Three Years before Current Fiscal Year	48,972	52,942
Four Years before Current Fiscal Year	29,372	40,907
Five Years before Current Fiscal Year	84,769	62,890
Revolving Loans Amortized Cost Basis	110,748	112,004
Total	1,133,782	1,207,391
Construction | Special Mention
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	469
Before Current Fiscal Year	160	1,485
Two Years before Current Fiscal Year	0	2,197
Three Years before Current Fiscal Year	0	1,221
Four Years before Current Fiscal Year	1,209	729
Five Years before Current Fiscal Year	734	13
Revolving Loans Amortized Cost Basis	0	0
Total	2,103	6,114
Construction | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	573
Before Current Fiscal Year	32	1,755
Two Years before Current Fiscal Year	2,199	3,178
Three Years before Current Fiscal Year	3,967	141
Four Years before Current Fiscal Year	124	0
Five Years before Current Fiscal Year	2,757	3,068
Revolving Loans Amortized Cost Basis	201	0
Total	9,280	8,715
Residential real estate | 1-to-4 family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	203,763	284,978
Before Current Fiscal Year	242,754	179,968
Two Years before Current Fiscal Year	155,236	169,514
Three Years before Current Fiscal Year	130,607	163,957
Four Years before Current Fiscal Year	135,593	115,537
Five Years before Current Fiscal Year	258,670	175,316
Revolving Loans Amortized Cost Basis	0	0
Total	1,126,623	1,089,270
Residential real estate | 1-to-4 family mortgage | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	203,719	283,107
Before Current Fiscal Year	241,270	176,711
Two Years before Current Fiscal Year	152,228	164,499
Three Years before Current Fiscal Year	126,627	157,731
Four Years before Current Fiscal Year	130,028	111,194
Five Years before Current Fiscal Year	246,202	162,051
Revolving Loans Amortized Cost Basis	0	0
Total	1,100,074	1,055,293
Residential real estate | 1-to-4 family mortgage | Special Mention
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	44	1,423
Before Current Fiscal Year	1,145	1,829
Two Years before Current Fiscal Year	1,201	1,209
Three Years before Current Fiscal Year	606	753
Four Years before Current Fiscal Year	328	721
Five Years before Current Fiscal Year	2,752	3,865
Revolving Loans Amortized Cost Basis	0	0
Total	6,076	9,800
Residential real estate | 1-to-4 family mortgage | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	448
Before Current Fiscal Year	339	1,428
Two Years before Current Fiscal Year	1,807	3,806
Three Years before Current Fiscal Year	3,374	5,473
Four Years before Current Fiscal Year	5,237	3,622
Five Years before Current Fiscal Year	9,716	9,400
Revolving Loans Amortized Cost Basis	0	0
Total	20,473	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	401,343	408,211
Total	401,343	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	396,297	400,206
Total	396,297	400,206
Residential real estate | Residential line of credit | Special Mention
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	344	2,653
Total	344	2,653
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	4,702	5,352
Total	4,702	5,352
Residential real estate | Multi-family mortgage
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	143,092	29,006
Before Current Fiscal Year	31,127	13,446
Two Years before Current Fiscal Year	74,713	11,843
Three Years before Current Fiscal Year	7,370	46,561
Four Years before Current Fiscal Year	39,365	28,330
Five Years before Current Fiscal Year	57,479	35,396
Revolving Loans Amortized Cost Basis	10,454	11,094
Total	363,600	175,676
Residential real estate | Multi-family mortgage | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	143,092	29,006
Before Current Fiscal Year	31,127	13,446
Two Years before Current Fiscal Year	74,713	11,843
Three Years before Current Fiscal Year	7,370	46,561
Four Years before Current Fiscal Year	39,365	28,330
Five Years before Current Fiscal Year	57,426	35,339
Revolving Loans Amortized Cost Basis	10,454	11,094
Total	363,547	175,619
Residential real estate | Multi-family mortgage | Special Mention
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	0	0
Total	0	0
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	53	57
Revolving Loans Amortized Cost Basis	0	0
Total	53	57
Commercial real estate | Owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	64,153	141,915
Before Current Fiscal Year	138,004	182,641
Two Years before Current Fiscal Year	192,328	104,251
Three Years before Current Fiscal Year	95,674	116,906
Four Years before Current Fiscal Year	95,793	82,914
Five Years before Current Fiscal Year	276,844	237,800
Revolving Loans Amortized Cost Basis	60,809	58,414
Total	923,605	924,841
Commercial real estate | Owner occupied | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	64,153	140,904
Before Current Fiscal Year	138,004	179,500
Two Years before Current Fiscal Year	187,870	97,577
Three Years before Current Fiscal Year	89,391	94,659
Four Years before Current Fiscal Year	90,172	76,539
Five Years before Current Fiscal Year	256,949	224,108
Revolving Loans Amortized Cost Basis	58,761	53,451
Total	885,300	866,738
Commercial real estate | Owner occupied | Special Mention
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	967
Before Current Fiscal Year	0	1,356
Two Years before Current Fiscal Year	1,335	4,251
Three Years before Current Fiscal Year	3,649	16,173
Four Years before Current Fiscal Year	1,464	6,101
Five Years before Current Fiscal Year	5,749	2,466
Revolving Loans Amortized Cost Basis	288	230
Total	12,485	31,544
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	3,123	2,423
Three Years before Current Fiscal Year	2,634	6,074
Four Years before Current Fiscal Year	4,157	274
Five Years before Current Fiscal Year	14,146	11,226
Revolving Loans Amortized Cost Basis	1,760	4,733
Total	25,820	26,559
Commercial real estate | Non-owner occupied
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	226,622	166,962
Before Current Fiscal Year	162,080	233,152
Two Years before Current Fiscal Year	170,733	350,814
Three Years before Current Fiscal Year	328,189	221,149
Four Years before Current Fiscal Year	204,119	290,370
Five Years before Current Fiscal Year	528,479	297,712
Revolving Loans Amortized Cost Basis	54,992	38,820
Total	1,675,214	1,598,979
Commercial real estate | Non-owner occupied | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	226,622	166,962
Before Current Fiscal Year	162,080	229,442
Two Years before Current Fiscal Year	166,597	342,640
Three Years before Current Fiscal Year	300,073	221,149
Four Years before Current Fiscal Year	202,577	290,163
Five Years before Current Fiscal Year	505,746	272,184
Revolving Loans Amortized Cost Basis	54,947	38,820
Total	1,618,642	1,561,360
Commercial real estate | Non-owner occupied | Special Mention
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	0	0
Before Current Fiscal Year	0	1,500
Two Years before Current Fiscal Year	0	6,672
Three Years before Current Fiscal Year	3,500	0
Four Years before Current Fiscal Year	0	207
Five Years before Current Fiscal Year	8,278	8,445
Revolving Loans Amortized Cost Basis	0	0
Total	11,778	16,824
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	4,136	1,502
Three Years before Current Fiscal Year	24,616	0
Four Years before Current Fiscal Year	1,542	0
Five Years before Current Fiscal Year	14,455	17,083
Revolving Loans Amortized Cost Basis	45	0
Total	44,794	20,795
Consumer and other
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	56,760	90,057
Before Current Fiscal Year	66,117	54,201
Two Years before Current Fiscal Year	45,080	42,747
Three Years before Current Fiscal Year	37,147	28,830
Four Years before Current Fiscal Year	24,658	44,964
Five Years before Current Fiscal Year	79,789	41,345
Revolving Loans Amortized Cost Basis	14,913	15,496
Total	324,464	317,640
Consumer and other | Pass
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	56,647	89,625
Before Current Fiscal Year	65,973	52,839
Two Years before Current Fiscal Year	44,844	39,725
Three Years before Current Fiscal Year	36,124	27,201
Four Years before Current Fiscal Year	23,731	43,503
Five Years before Current Fiscal Year	76,402	37,673
Revolving Loans Amortized Cost Basis	14,476	14,817
Total	318,197	305,383
Consumer and other | Special Mention
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	75	281
Before Current Fiscal Year	0	797
Two Years before Current Fiscal Year	14	1,588
Three Years before Current Fiscal Year	0	468
Four Years before Current Fiscal Year	1	526
Five Years before Current Fiscal Year	522	1,364
Revolving Loans Amortized Cost Basis	0	11
Total	612	5,035
Consumer and other | Classified
Financing Receivable, Allowance for Credit Loss [Line Items]
Current Fiscal Year	38	151
Before Current Fiscal Year	144	565
Two Years before Current Fiscal Year	222	1,434
Three Years before Current Fiscal Year	1,023	1,161
Four Years before Current Fiscal Year	926	935
Five Years before Current Fiscal Year	2,865	2,308
Revolving Loans Amortized Cost Basis	437	668
Total	$ 5,655	$ 7,222