Loans and allowance for credit losses - Analysis of Aging by Class of Financing Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Loans	$ 7,604,662	$ 7,082,959
90 days or  more and accruing interest	11,735	13,696
Non-accrual loans	35,568	50,760
30-89 days past due
Financing Receivable, Past Due [Line Items]
Loans	26,450	26,995
Loans current on payments and accruing interest
Financing Receivable, Past Due [Line Items]
Loans	7,530,909	6,991,508
Commercial and industrial
Financing Receivable, Past Due [Line Items]
Loans	1,290,565	1,346,122
90 days or  more and accruing interest	63	330
Non-accrual loans	1,520	16,005
Commercial and industrial | 30-89 days past due
Financing Receivable, Past Due [Line Items]
Loans	1,030	3,297
Commercial and industrial | Loans current on payments and accruing interest
Financing Receivable, Past Due [Line Items]
Loans	1,287,952	1,326,490
Construction
Financing Receivable, Past Due [Line Items]
Loans	1,327,659	1,222,220
90 days or  more and accruing interest	718	573
Non-accrual loans	3,622	4,053
Construction | 30-89 days past due
Financing Receivable, Past Due [Line Items]
Loans	4,852	7,607
Construction | Loans current on payments and accruing interest
Financing Receivable, Past Due [Line Items]
Loans	1,318,467	1,209,987
Residential real estate | 1-to-4 family mortgage
Financing Receivable, Past Due [Line Items]
Loans	1,270,467	1,089,270
90 days or  more and accruing interest	9,363	10,470
Non-accrual loans	4,593	5,923
Residential real estate | 1-to-4 family mortgage | 30-89 days past due
Financing Receivable, Past Due [Line Items]
Loans	11,007	7,058
Residential real estate | 1-to-4 family mortgage | Loans current on payments and accruing interest
Financing Receivable, Past Due [Line Items]
Loans	1,245,504	1,065,819
Residential real estate | Residential line of credit
Financing Receivable, Past Due [Line Items]
Loans	383,039	408,211
90 days or  more and accruing interest	0	239
Non-accrual loans	1,736	1,757
Residential real estate | Residential line of credit | 30-89 days past due
Financing Receivable, Past Due [Line Items]
Loans	319	3,551
Residential real estate | Residential line of credit | Loans current on payments and accruing interest
Financing Receivable, Past Due [Line Items]
Loans	380,984	402,664
Residential real estate | Multi-family mortgage
Financing Receivable, Past Due [Line Items]
Loans	326,551	175,676
90 days or  more and accruing interest	0	57
Non-accrual loans	49	0
Residential real estate | Multi-family mortgage | 30-89 days past due
Financing Receivable, Past Due [Line Items]
Loans	0	0
Residential real estate | Multi-family mortgage | Loans current on payments and accruing interest
Financing Receivable, Past Due [Line Items]
Loans	326,502	175,619
Commercial real estate | Owner occupied
Financing Receivable, Past Due [Line Items]
Loans	951,582	924,841
90 days or  more and accruing interest	0	0
Non-accrual loans	6,710	7,948
Commercial real estate | Owner occupied | 30-89 days past due
Financing Receivable, Past Due [Line Items]
Loans	1,417	98
Commercial real estate | Owner occupied | Loans current on payments and accruing interest
Financing Receivable, Past Due [Line Items]
Loans	943,455	916,795
Commercial real estate | Non-owner occupied
Financing Receivable, Past Due [Line Items]
Loans	1,730,165	1,598,979
90 days or  more and accruing interest	0	0
Non-accrual loans	14,084	12,471
Commercial real estate | Non-owner occupied | 30-89 days past due
Financing Receivable, Past Due [Line Items]
Loans	427	915
Commercial real estate | Non-owner occupied | Loans current on payments and accruing interest
Financing Receivable, Past Due [Line Items]
Loans	1,715,654	1,585,593
Consumer and other
Financing Receivable, Past Due [Line Items]
Loans	324,634	317,640
90 days or  more and accruing interest	1,591	2,027
Non-accrual loans	3,254	2,603
Consumer and other | 30-89 days past due
Financing Receivable, Past Due [Line Items]
Loans	7,398	4,469
Consumer and other | Loans current on payments and accruing interest
Financing Receivable, Past Due [Line Items]
Loans	$ 312,391	$ 308,541