Assets and Liabilities Measured at Fair Value - Assets and liabilities measured at fair value on recurring basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Debt securities available-for-sale	$ 2,690,448	$ 2,274,581
Mortgage loans held for sale	128,587	58,484
U.S. Treasuries
Assets:
Debt securities available-for-sale	128,534	154,618
State and political subdivisions
Assets:
Debt securities available-for-sale	259,176	226,490
Residential mortgage-backed securities
Assets:
Debt securities available-for-sale	1,299,804
Commercial mortgage-backed securities
Assets:
Debt securities available-for-sale	394,517
Corporate bonds
Assets:
Debt securities available-for-sale	99,270	203,091
Asset-backed securities
Assets:
Debt securities available-for-sale	457,402	103,369
Recurring
Assets:
Equity securities with readily available fair values	1,403	1,973
Mortgage loans held for sale	128,587	58,484
Deferred compensation plan assets	9,001	8,133
Servicing rights for SBA/USDA loans	6,761	6,794
Residential mortgage servicing rights	14,367	13,565
Derivative financial instruments	103,388	35,007
Total assets	2,953,955	2,398,537
Liabilities:
Deferred compensation plan liability	9,007	8,132
Derivative financial instruments	33,519	15,516
Total liabilities	42,526	23,648
Recurring \| U.S. Treasuries
Assets:
Debt securities available-for-sale	128,534	154,618
Recurring \| U.S. Government agencies
Assets:
Debt securities available-for-sale	51,745	3,035
Recurring \| State and political subdivisions
Assets:
Debt securities available-for-sale	259,176	226,490
Recurring \| Residential mortgage-backed securities
Assets:
Debt securities available-for-sale	1,299,804	1,299,025
Recurring \| Commercial mortgage-backed securities
Assets:
Debt securities available-for-sale	394,517	284,953
Recurring \| Corporate bonds
Assets:
Debt securities available-for-sale	99,270	203,091
Recurring \| Asset-backed securities
Assets:
Debt securities available-for-sale	457,402	103,369
Recurring \| Level 1
Assets:
Equity securities with readily available fair values	573	1,973
Mortgage loans held for sale	0	0
Deferred compensation plan assets	9,001	8,133
Servicing rights for SBA/USDA loans	0	0
Residential mortgage servicing rights	0	0
Derivative financial instruments	0	0
Total assets	138,108	164,724
Liabilities:
Deferred compensation plan liability	9,007	8,132
Derivative financial instruments	0	0
Total liabilities	9,007	8,132
Recurring \| Level 1 \| U.S. Treasuries
Assets:
Debt securities available-for-sale	128,534	154,618
Recurring \| Level 1 \| U.S. Government agencies
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 1 \| State and political subdivisions
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 1 \| Residential mortgage-backed securities
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 1 \| Commercial mortgage-backed securities
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 1 \| Corporate bonds
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 1 \| Asset-backed securities
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 2
Assets:
Equity securities with readily available fair values	830	0
Mortgage loans held for sale	128,587	58,484
Deferred compensation plan assets	0	0
Servicing rights for SBA/USDA loans	0	0
Residential mortgage servicing rights	0	0
Derivative financial instruments	90,590	27,769
Total assets	2,780,171	2,205,218
Liabilities:
Deferred compensation plan liability	0	0
Derivative financial instruments	31,037	6,957
Total liabilities	31,037	6,957
Recurring \| Level 2 \| U.S. Treasuries
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 2 \| U.S. Government agencies
Assets:
Debt securities available-for-sale	51,745	3,035
Recurring \| Level 2 \| State and political subdivisions
Assets:
Debt securities available-for-sale	259,176	226,490
Recurring \| Level 2 \| Residential mortgage-backed securities
Assets:
Debt securities available-for-sale	1,299,804	1,299,025
Recurring \| Level 2 \| Commercial mortgage-backed securities
Assets:
Debt securities available-for-sale	394,517	284,953
Recurring \| Level 2 \| Corporate bonds
Assets:
Debt securities available-for-sale	97,520	202,093
Recurring \| Level 2 \| Asset-backed securities
Assets:
Debt securities available-for-sale	457,402	103,369
Recurring \| Level 3
Assets:
Equity securities with readily available fair values	0	0
Mortgage loans held for sale	0	0
Deferred compensation plan assets	0	0
Servicing rights for SBA/USDA loans	6,761	6,794
Residential mortgage servicing rights	14,367	13,565
Derivative financial instruments	12,798	7,238
Total assets	35,676	28,595
Liabilities:
Deferred compensation plan liability	0	0
Derivative financial instruments	2,482	8,559
Total liabilities	2,482	8,559
Recurring \| Level 3 \| U.S. Treasuries
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 3 \| U.S. Government agencies
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 3 \| State and political subdivisions
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 3 \| Residential mortgage-backed securities
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 3 \| Commercial mortgage-backed securities
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 3 \| Corporate bonds
Assets:
Debt securities available-for-sale	1,750	998
Recurring \| Level 3 \| Asset-backed securities
Assets:
Debt securities available-for-sale	$ 0	$ 0

Residential Mortgage Servicing Asset At Fair Value, Amount

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

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

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Fair value of financial and nonfinancial obligations.

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Fair value portion of mortgage loans held-for-sale.

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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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