Fair Value Measurements - Assets and liabilities measured at fair value on recurring basis (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Assets:
Debt securities available-for-sale	$ 2,274,581	$ 2,628,467
Mortgage loans held for sale	58,500	18,900
Derivative financial instruments	35,007	24,705
Liabilities, Fair Value Disclosure [Abstract]
Derivative financial instruments	15,516	26,433
U.S. Treasuries
Assets:
Debt securities available-for-sale	154,618	149,307
U.S. Government agencies
Assets:
Debt securities available-for-sale	3,035	25,553
State and political subdivisions
Assets:
Debt securities available-for-sale	226,490	233,941
Residential mortgage-backed securities
Assets:
Debt securities available-for-sale	1,299,025
Commercial mortgage-backed securities
Assets:
Debt securities available-for-sale	284,953
Corporate bonds
Assets:
Debt securities available-for-sale	203,091	199,163
Asset-backed securities
Assets:
Debt securities available-for-sale	103,369	182,676
Recurring
Assets:
Mortgage loans held for sale	58,484	18,935
Deferred compensation plan assets	8,133	6,404
Servicing rights for SBA/USDA loans	6,794	7,510
Residential mortgage servicing rights	13,565	11,877
Derivative financial instruments	35,007	24,705
Total assets	2,398,537	2,698,974
Liabilities, Fair Value Disclosure [Abstract]
Deferred compensation plan liability	8,132	6,404
Derivative financial instruments	15,516	26,433
Total liabilities	23,648	32,837
Recurring \| U.S. Treasuries
Assets:
Debt securities available-for-sale	154,618	149,307
Recurring \| U.S. Government agencies
Assets:
Debt securities available-for-sale	3,035	25,553
Recurring \| State and political subdivisions
Assets:
Debt securities available-for-sale	226,490	233,941
Recurring \| Residential mortgage-backed securities
Assets:
Debt securities available-for-sale	1,299,025	1,445,910
Recurring \| Commercial mortgage-backed securities
Assets:
Debt securities available-for-sale	284,953	391,917
Recurring \| Corporate bonds
Assets:
Debt securities available-for-sale	203,091	199,163
Recurring \| Asset-backed securities
Assets:
Debt securities available-for-sale	103,369	182,676
Recurring \| Equity securities with readily determinable fair values
Assets:
Debt securities available-for-sale	1,973	1,076
Recurring \| Level 1
Assets:
Mortgage loans held for sale	0	0
Deferred compensation plan assets	8,133	6,404
Servicing rights for SBA/USDA loans	0	0
Residential mortgage servicing rights	0	0
Derivative financial instruments	0	0
Total assets	164,724	156,787
Liabilities, Fair Value Disclosure [Abstract]
Deferred compensation plan liability	8,132	6,404
Derivative financial instruments	0	0
Total liabilities	8,132	6,404
Recurring \| Level 1 \| U.S. Treasuries
Assets:
Debt securities available-for-sale	154,618	149,307
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 1 \| Equity securities with readily determinable fair values
Assets:
Debt securities available-for-sale	1,973	1,076
Recurring \| Level 2
Assets:
Mortgage loans held for sale	58,484	18,935
Deferred compensation plan assets	0	0
Servicing rights for SBA/USDA loans	0	0
Residential mortgage servicing rights	0	0
Derivative financial instruments	27,769	12,864
Total assets	2,205,218	2,509,964
Liabilities, Fair Value Disclosure [Abstract]
Deferred compensation plan liability	0	0
Derivative financial instruments	6,957	10,701
Total liabilities	6,957	10,701
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	3,035	25,553
Recurring \| Level 2 \| State and political subdivisions
Assets:
Debt securities available-for-sale	226,490	233,941
Recurring \| Level 2 \| Residential mortgage-backed securities
Assets:
Debt securities available-for-sale	1,299,025	1,445,910
Recurring \| Level 2 \| Commercial mortgage-backed securities
Assets:
Debt securities available-for-sale	284,953	391,917
Recurring \| Level 2 \| Corporate bonds
Assets:
Debt securities available-for-sale	202,093	198,168
Recurring \| Level 2 \| Asset-backed securities
Assets:
Debt securities available-for-sale	103,369	182,676
Recurring \| Level 2 \| Equity securities with readily determinable fair values
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 3
Assets:
Mortgage loans held for sale	0	0
Deferred compensation plan assets	0	0
Servicing rights for SBA/USDA loans	6,794	7,510
Residential mortgage servicing rights	13,565	11,877
Derivative financial instruments	7,238	11,841
Total assets	28,595	32,223
Liabilities, Fair Value Disclosure [Abstract]
Deferred compensation plan liability	0	0
Derivative financial instruments	8,559	15,732
Total liabilities	8,559	15,732
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	998	995
Recurring \| Level 3 \| Asset-backed securities
Assets:
Debt securities available-for-sale	0	0
Recurring \| Level 3 \| Equity securities with readily determinable fair values
Assets:
Debt securities available-for-sale	$ 0	$ 0

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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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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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Fair value of financial and nonfinancial obligations.

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