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Reclassification Adjustments Out of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Reclassification Adjustments out of AOCI [Abstract] |  |  |
Net securities (gains) losses | $ 388 | $ (4,213) | $ 6,341
Interest income (expense) | 315,678 | 311,555 | 305,629
Other noninterest expense | 24,863 | 24,440 | 19,597
Income tax (benefit) expense | 28,699 | 34,411 | 24,436
Net Income | 104,388 | 121,021 | 112,566
Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |
Reclassification Adjustments out of AOCI [Abstract] |  |  |
Total reclassifications, net of tax | 1,923 | 1,117 | 4,617
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |
Reclassification Adjustments out of AOCI [Abstract] |  |  |
Income tax (benefit) expense | (160) | (204) | (1,827)
Net Income | 481 | 612 | 5,483
Gains (losses) on AFS securities [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |
Reclassification Adjustments out of AOCI [Abstract] |  |  |
Net securities (gains) losses | (3) | 79 | 6,622
Amortization of Unrealized Gains Related to Securities Transfer [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |
Reclassification Adjustments out of AOCI [Abstract] |  |  |
Interest income (expense) | 644 | 737 | 688
Net Unrealized Losses (Gains) on Cash Flow Hedges Reclassified to Interest Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |
Reclassification Adjustments out of AOCI [Abstract] |  |  |
Interest income (expense) | 296 | (2,012) | (2,300)
Income tax (benefit) expense | (74) | 503 | 575
Net Income | 222 | (1,509) | (1,725)
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |
Reclassification Adjustments out of AOCI [Abstract] |  |  |
Income tax (benefit) expense | (407) | (672) | (286)
Net Income | 1,220 | 2,014 | 859
Amortization of Net Losses [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |
Reclassification Adjustments out of AOCI [Abstract] |  |  |
Other noninterest expense | 1,535 | 2,593 | 1,054
Amortization of Prior Service Costs [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] |  |  |
Reclassification Adjustments out of AOCI [Abstract] |  |  |
Other noninterest expense | $ 92 | $ 93 | $ 91

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