FAIR VALUE - Financial assets and liabilities accounted for at fair value on a recurring basis (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2025	Dec. 31, 2024
Available-for-sale investment securities
Fair Value	$ 2,859,312	$ 2,785,714
Unpaid principal value of mortgage loans held for sale	300	1,500
Fair value, assets, levels transfers	0
Transfers between Level 2 and Level 1	0
Transfers in of level 3	0
Transfers out of level 3	0
U.S. Treasury and agency securities
Available-for-sale investment securities
Fair Value	2,177,910	2,083,786
Obligations of state and political subdivisions
Available-for-sale investment securities
Fair Value	385,441	386,495
Government agency mortgage-backed securities
Available-for-sale investment securities
Fair Value	286,249	301,224
Corporate debt securities
Available-for-sale investment securities
Fair Value	4,875	7,697
Government agency collateralized mortgage obligations
Available-for-sale investment securities
Fair Value	4,837	6,512
Recurring
Available-for-sale investment securities
Fair Value	2,859,312	2,785,714
Equity securities	2,905	2,354
Mortgage loans held for sale	339	1,470
Total	2,862,725	2,789,745
Recurring \| Commitments to originate real estate loans for sale
Available-for-sale investment securities
Derivative asset	169	215
Recurring \| Interest rate swap agreements
Available-for-sale investment securities
Derivative asset	7,823	2,664
Derivative liability	(7,823)	(2,664)
Recurring \| Forward sales commitments
Available-for-sale investment securities
Derivative asset		(8)
Recurring \| U.S. Treasury and agency securities
Available-for-sale investment securities
Fair Value	2,177,910	2,083,786
Recurring \| Obligations of state and political subdivisions
Available-for-sale investment securities
Fair Value	385,441	386,495
Recurring \| Government agency mortgage-backed securities
Available-for-sale investment securities
Fair Value	286,249	301,224
Recurring \| Corporate debt securities
Available-for-sale investment securities
Fair Value	4,875	7,697
Recurring \| Government agency collateralized mortgage obligations
Available-for-sale investment securities
Fair Value	4,837	6,512
Recurring \| Level 1
Available-for-sale investment securities
Fair Value	2,116,941	2,025,164
Equity securities	2,905	2,354
Mortgage loans held for sale	0	0
Total	2,119,846	2,027,518
Recurring \| Level 1 \| Commitments to originate real estate loans for sale
Available-for-sale investment securities
Derivative asset	0	0
Recurring \| Level 1 \| Interest rate swap agreements
Available-for-sale investment securities
Derivative asset	0	0
Derivative liability	0	0
Recurring \| Level 1 \| Forward sales commitments
Available-for-sale investment securities
Derivative asset		0
Recurring \| Level 1 \| U.S. Treasury and agency securities
Available-for-sale investment securities
Fair Value	2,116,941	2,025,164
Recurring \| Level 1 \| Obligations of state and political subdivisions
Available-for-sale investment securities
Fair Value	0	0
Recurring \| Level 1 \| Government agency mortgage-backed securities
Available-for-sale investment securities
Fair Value	0	0
Recurring \| Level 1 \| Corporate debt securities
Available-for-sale investment securities
Fair Value	0	0
Recurring \| Level 1 \| Government agency collateralized mortgage obligations
Available-for-sale investment securities
Fair Value	0	0
Recurring \| Level 2
Available-for-sale investment securities
Fair Value	742,371	760,550
Equity securities	0	0
Mortgage loans held for sale	339	1,470
Total	742,710	762,012
Recurring \| Level 2 \| Commitments to originate real estate loans for sale
Available-for-sale investment securities
Derivative asset	0	0
Recurring \| Level 2 \| Interest rate swap agreements
Available-for-sale investment securities
Derivative asset	7,823	2,664
Derivative liability	(7,823)	(2,664)
Recurring \| Level 2 \| Forward sales commitments
Available-for-sale investment securities
Derivative asset		(8)
Recurring \| Level 2 \| U.S. Treasury and agency securities
Available-for-sale investment securities
Fair Value	60,969	58,622
Recurring \| Level 2 \| Obligations of state and political subdivisions
Available-for-sale investment securities
Fair Value	385,441	386,495
Recurring \| Level 2 \| Government agency mortgage-backed securities
Available-for-sale investment securities
Fair Value	286,249	301,224
Recurring \| Level 2 \| Corporate debt securities
Available-for-sale investment securities
Fair Value	4,875	7,697
Recurring \| Level 2 \| Government agency collateralized mortgage obligations
Available-for-sale investment securities
Fair Value	4,837	6,512
Recurring \| Level 3
Available-for-sale investment securities
Fair Value	0	0
Equity securities	0	0
Mortgage loans held for sale	0	0
Total	169	215
Recurring \| Level 3 \| Commitments to originate real estate loans for sale
Available-for-sale investment securities
Derivative asset	169	215
Recurring \| Level 3 \| Interest rate swap agreements
Available-for-sale investment securities
Derivative asset	0	0
Derivative liability	0	0
Recurring \| Level 3 \| Forward sales commitments
Available-for-sale investment securities
Derivative asset		0
Recurring \| Level 3 \| U.S. Treasury and agency securities
Available-for-sale investment securities
Fair Value	0	0
Recurring \| Level 3 \| Obligations of state and political subdivisions
Available-for-sale investment securities
Fair Value	0	0
Recurring \| Level 3 \| Government agency mortgage-backed securities
Available-for-sale investment securities
Fair Value	0	0
Recurring \| Level 3 \| Corporate debt securities
Available-for-sale investment securities
Fair Value	0	0
Recurring \| Level 3 \| Government agency collateralized mortgage obligations
Available-for-sale investment securities
Fair Value	$ 0	$ 0

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

No definition available.

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- Definition

Amount of transfers of liabilities measured on a recurring basis out of Levels 2 of the fair value hierarchy into Level 1.

+ References

No definition available.

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- Definition

Amount of unpaid principal value of mortgage loans held-for sale.

+ References

No definition available.

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Period Type:	instant

- References

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- Definition

Amount excluding accrued interest, 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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