DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES - Derivative Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Jun. 30, 2023	Dec. 31, 2022
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 4,539,818	$ 4,524,514
Estimated Fair Value Asset (Liability)	(41,920)	(43,167)
Impact of settled to market contracts	31,000	38,300
Interest rate swaps
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	6,600
Cash flow hedges
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	800,000	800,000
Estimated Fair Value Asset (Liability)	1,495	1,937
Cash flow hedges \| Interest rate swaps \| Commercial loan
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 600,000	$ 400,000
Weighted Average Maturity (In years)	2 years 4 months 24 days	2 years 8 months 12 days
Weighted Average Rate, Received	5.07%	4.09%
Weighted Average Rate, Contract pay rate	3.64%	3.51%
Estimated Fair Value Asset (Liability)	$ 714	$ 0
Cash flow hedges \| Forward starting interest rate swaps \| Commercial loan
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount		$ 200,000
Weighted Average Maturity (In years)		3 years 3 months 18 days
Weighted Average Rate, Received		0.00%
Weighted Average Rate, Contract pay rate		3.90%
Estimated Fair Value Asset (Liability)		$ 0
Cash flow hedges \| Interest rate collars \| Commercial loan
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 200,000	$ 200,000
Weighted Average Maturity (In years)	3 years	3 years 6 months
Estimated Fair Value Asset (Liability)	$ 781	$ 1,937
Economic hedges \| Cash flow hedges \| Interest rate swaps
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	800,000
Economic hedges \| Economic hedges
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	3,730,449	3,720,400
Estimated Fair Value Asset (Liability)	(43,452)	(45,121)
Economic hedges \| Economic hedges \| Interest rate swaps
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	3,400,000
Economic hedges \| Economic hedges \| Interest rate swaps \| Commercial loan
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 1,683,400	$ 1,685,263
Weighted Average Maturity (In years)	5 years 3 months 18 days	5 years 8 months 12 days
Weighted Average Rate, Received	4.16%	4.11%
Weighted Average Rate, Contract pay rate	6.28%	5.55%
Estimated Fair Value Asset (Liability)	$ (92,320)	$ (95,114)
Economic hedges \| Economic hedges \| Interest rate swaps \| Interest rate swap on tax advantaged economic development bond
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 6,637	$ 7,062
Weighted Average Maturity (In years)	6 years 4 months 24 days	6 years 10 months 24 days
Weighted Average Rate, Received	4.55%	4.49%
Weighted Average Rate, Contract pay rate	5.09%	5.09%
Estimated Fair Value Asset (Liability)	$ (118)	$ (193)
Economic hedges \| Economic hedges \| Reverse interest rate swaps \| Commercial loan
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 1,683,400	$ 1,685,263
Weighted Average Maturity (In years)	5 years 3 months 18 days	5 years 8 months 12 days
Weighted Average Rate, Received	6.28%	5.55%
Weighted Average Rate, Contract pay rate	4.16%	4.11%
Estimated Fair Value Asset (Liability)	$ 49,004	$ 50,267
Economic hedges \| Economic hedges \| Risk participation agreements with dealer banks
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 348,136	$ 341,885
Weighted Average Maturity (In years)	4 years 1 month 6 days	6 years 7 months 6 days
Estimated Fair Value Asset (Liability)	$ (81)	$ (89)
Economic hedges \| Economic hedges \| Forward sale commitments
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 8,876	$ 927
Weighted Average Maturity (In years)	2 months 12 days	2 months 12 days
Estimated Fair Value Asset (Liability)	$ 63	$ 8
Non-hedging derivatives
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	9,369	4,114
Estimated Fair Value Asset (Liability)	37	17
Non-hedging derivatives \| Commitments to lend
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 9,369	$ 4,114
Weighted Average Maturity (In years)	2 months 12 days	2 months 12 days
Estimated Fair Value Asset (Liability)	$ 37	$ 17

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Represents information pertaining to the derivative weighted average rate which is received.

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-SubTopic 10
-Topic 815
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480463/815-10-45-5

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Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480434/815-10-50-1B

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
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-Publisher FASB
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