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Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
AFS Debt Securities: |  |  |
Unrealized holdings losses, pre-tax amount | $ 33,198 | $ 26,743 | $ (10,846)
Unrealized holdings losses, tax (expense) benefit | (7,138) | (5,750) | 2,332
Unrealized holdings losses, after-tax amount | 26,060 | 20,993 | (8,514)
Less: reclassification adjustment for realized losses, pre-tax amount | 0 | (105) | (663)
Less: reclassification adjustment for realized losses, tax (expense) benefit | 0 | 22 | 142
Less: reclassification adjustment for realized losses, after-tax amount | 0 | (83) | (521)
Net unrealized losses, pre-tax amount | 33,198 | 26,848 | (10,183)
Net unrealized losses, tax (expense) benefit | (7,138) | (5,772) | 2,190
Net unrealized losses, after-tax amount | 26,060 | 21,076 | (7,993)
Cash Flow Hedges: |  |  |
Net increase in fair value, pre-tax amount | 1,214 | (2,973) | 1,066
Net increase in fair value, tax (expense) benefit | (260) | 639 | (229)
Net increase in fair value, after-tax amount | 954 | (2,334) | 837
Less: effective portion reclassified into interest expense, pre-tax amount | (597) | (921) | (831)
Less: effective portion reclassified into interest expense, after-tax amount | (468) | (723) | (652)
Net increase in fair value, pre-tax amount | 1,811 | (2,052) | 1,897
Net increase in fair value, tax (expense) benefit | (389) | 441 | (408)
Net increase in fair value, after-tax amount | 1,422 | (1,611) | 1,489
Postretirement Plans: |  |  |
Net actuarial loss, pre-tax amount | (1,282) | (1,918) | 1,743
Net actuarial loss, tax (expense) benefit | 277 | 412 | (375)
Net actuarial loss, after-tax amount | (1,005) | (1,506) | 1,368
Less: Amortization of net actuarial losses, pre-tax amount | (701) | (271) | (613)
Less: Amortization of net actuarial losses, tax (expense) benefit | 151 | 59 | 131
Less: Amortization of net prior service credits, after-tax amount | (550) | (212) | (482)
Less: Amortization of net prior service credits, pre-tax amount | 24 | 24 | 24
Less: Amortization of net prior service credits, tax (expense) benefit | (5) | (5) | (5)
Less: Amortization of net prior service credits, after-tax amount | 19 | 19 | 19
Net loss on postretirement plans, pre-tax amount | (605) | (1,671) | 2,332
Net loss on postretirement plans, tax (expense) benefit | 131 | 358 | (501)
Net (loss) gain on postretirement plans, net of tax | (474) | (1,313) | 1,831
Other comprehensive income, pre-tax amount | 34,404 | 23,125 | (5,954)
Other comprehensive income, tax (expense) benefit | (7,396) | (4,973) | 1,281
Other comprehensive income (loss) | 27,008 | 18,152 | (4,673)
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Less: effective portion reclassified into interest expense, pre-tax amount | (597) | (921) | (831)
Less: Amounts reclassified from AOCI | (468) | (723) | (652)
Interest Expense, Borrowings and Subordinated Debentures |  |  |
Cash Flow Hedges: |  |  |
Less: effective portion reclassified into interest expense, pre-tax amount | (1,603) | (707) | (831)
Less: effective portion reclassified into interest expense, tax (expense) benefit | 345 | 151 | 179
Less: effective portion reclassified into interest expense, after-tax amount | (1,258) | (556) | (652)
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Less: effective portion reclassified into interest expense, pre-tax amount | (1,603) | (707) | (831)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax | (345) | (151) | (179)
Less: Amounts reclassified from AOCI | (1,258) | (556) | (652)
Interest Income, Interest and Fees on Loans |  |  |
Cash Flow Hedges: |  |  |
Less: effective portion reclassified into interest expense, pre-tax amount | 1,006 | (214) | 0
Less: effective portion reclassified into interest expense, tax (expense) benefit | (216) | 47 | 0
Less: effective portion reclassified into interest expense, after-tax amount | 790 | (167) | 0
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Less: effective portion reclassified into interest expense, pre-tax amount | 1,006 | (214) | 0
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax | 216 | (47) | 0
Less: Amounts reclassified from AOCI | $ 790 | $ (167) | $ 0

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