Fair value of financial instruments - Estimated Fair Values and Carrying Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Financial assets:
Net loans	$ 7,479,103	$ 6,912,570
Loans held for sale	752,223	899,173
Interest receivable	38,528	43,603
Derivatives	27,384	68,938
Financial liabilities:
Derivatives	21,000	48,242
Carrying amount
Financial assets:
Cash and cash equivalents	1,797,740	1,317,898
Investment securities	1,681,892	1,176,991
Net loans	7,479,103	6,912,570
Loans held for sale	752,223	899,173
Interest receivable	38,528	43,603
Mortgage servicing rights	115,512	79,997
Derivatives	27,384	68,938
Financial liabilities:
Deposits, Without stated maturities	9,705,816	8,020,783
Deposits, With stated maturities	1,131,081	1,437,254
Securities sold under agreement to repurchase and federal funds sold	40,716	32,199
Subordinated debt	129,544	189,527
Other borrowings		15,000
Interest payable	3,162	6,772
Derivatives	21,000	48,242
Fair Value
Financial assets:
Cash and cash equivalents	1,797,740	1,317,898
Investment securities	1,681,892	1,176,991
Net loans	7,566,717	7,058,693
Loans held for sale	752,223	899,173
Interest receivable	38,528	43,603
Mortgage servicing rights	115,512	79,997
Derivatives	27,384	68,938
Financial liabilities:
Deposits, Without stated maturities	9,705,816	8,020,783
Deposits, With stated maturities	1,137,647	1,446,605
Securities sold under agreement to repurchase and federal funds sold	40,716	32,199
Subordinated debt	133,021	192,149
Other borrowings		15,000
Interest payable	3,162	6,772
Derivatives	21,000	48,242
Fair Value \| Level 1
Financial assets:
Cash and cash equivalents	1,797,740	1,317,898
Investment securities	0	0
Net loans	0	0
Loans held for sale	0	0
Interest receivable	36	33
Mortgage servicing rights	0	0
Derivatives	0	0
Financial liabilities:
Deposits, Without stated maturities	9,705,816	8,020,783
Deposits, With stated maturities	0	0
Securities sold under agreement to repurchase and federal funds sold	40,716	32,199
Subordinated debt	0	0
Other borrowings		0
Interest payable	140	327
Derivatives	0	0
Fair Value \| Level 2
Financial assets:
Cash and cash equivalents	0	0
Investment securities	1,681,892	1,176,991
Net loans	0	0
Loans held for sale	672,924	683,770
Interest receivable	6,461	5,254
Mortgage servicing rights	0	0
Derivatives	27,384	68,938
Financial liabilities:
Deposits, Without stated maturities	0	0
Deposits, With stated maturities	1,137,647	1,446,605
Securities sold under agreement to repurchase and federal funds sold	0	0
Subordinated debt	0	0
Other borrowings		15,000
Interest payable	1,510	4,210
Derivatives	21,000	48,242
Fair Value \| Level 3
Financial assets:
Cash and cash equivalents	0	0
Investment securities	0	0
Net loans	7,566,717	7,058,693
Loans held for sale	79,299	215,403
Interest receivable	32,031	38,316
Mortgage servicing rights	115,512	79,997
Derivatives	0	0
Financial liabilities:
Deposits, Without stated maturities	0	0
Deposits, With stated maturities	0	0
Securities sold under agreement to repurchase and federal funds sold	0	0
Subordinated debt	133,021	192,149
Other borrowings		0
Interest payable	1,512	2,235
Derivatives	$ 0	$ 0

Deposits with stated maturities fair value disclosure.

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Deposits without stated maturities fair value disclosure.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Amount excluding accrued interest, after allowance for credit loss, of financing receivable.

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Amount of interest payable on debt, including, but not limited to, trade payables.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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The carrying amount as of the balance sheet date for the aggregate of other miscellaneous borrowings owed by the reporting entity.

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Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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