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Reclassification Adjustments Out of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Reclassification Adjustment out of AOCI [Abstract] |  |  |  |
Net securities (gains) losses | $ (100) | $ 84 | $ 568 | $ (548)
Interest income (expense) | 77,674 | 77,943 | 235,907 | 235,570
Other noninterest expense | 6,232 | 3,857 | 14,405 | 14,730
Income tax (benefit) | 11,043 | 10,988 | 34,193 | 19,267
Net income | 37,433 | 35,113 | 117,575 | 70,194
Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |  |
Reclassification Adjustment out of AOCI [Abstract] |  |  |  |
Total reclassifications during the period, net of tax | 369 | 480 | 1,088 | 1,370
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |  |
Reclassification Adjustment out of AOCI [Abstract] |  |  |  |
Income tax (benefit) | (38) | (39) | (109) | (123)
Net income | 111 | 118 | 325 | 369
Gains on AFS Securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |  |
Reclassification Adjustment out of AOCI [Abstract] |  |  |  |
Net securities (gains) losses | 0 | 0 | 0 | (3)
Amortization of Unrealized Gains Related to Securities Transfer [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |  |
Reclassification Adjustment out of AOCI [Abstract] |  |  |  |
Interest income (expense) | 149 | 157 | 434 | 495
Net Unrealized Losses on Cash Flow Hedges Reclassified to Interest Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |  |
Reclassification Adjustment out of AOCI [Abstract] |  |  |  |
Interest income (expense) | 0 | 101 | 21 | 192
Income tax (benefit) | 0 | (25) | (5) | (48)
Net income | 0 | 76 | 16 | 144
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |  |
Reclassification Adjustment out of AOCI [Abstract] |  |  |  |
Income tax (benefit) | (86) | (95) | (249) | (286)
Net income | 258 | 286 | 747 | 857
Amortization of Net Losses [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |  |
Reclassification Adjustment out of AOCI [Abstract] |  |  |  |
Other noninterest expense | 317 | 359 | 913 | 1,075
Amortization of Prior Service Costs [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |  |
Reclassification Adjustment out of AOCI [Abstract] |  |  |  |
Other noninterest expense | $ 27 | $ 22 | $ 83 | $ 68

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