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DERIVATIVES AND HEDGING ACTIVITIES - Narrative (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
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Derivative [Line Items] |  |
Liability for cash collateral received from counterparties | $ 2,600 | $ 3,300
Receivable for cash collateral paid to counterparties | 8,200 | 16,500
Notional amount of open interest rate swap agreements | 1,601,281 | 2,322,816
Interest rate swaps, back-to-back |  |
Derivative [Line Items] |  |
Notional amount of open interest rate swap agreements | $ 275,000 | $ 246,000

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