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Other Comprehensive Income (Loss) - Components of Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Debt Securities: |  |  |
Unrealized holdings losses, pre-tax amount | $ 13,646 | $ (172,699) | $ (38,832)
Unrealized holdings losses, tax (expense) benefit | (2,932) | 37,131 | 8,349
Unrealized holdings losses, after-tax amount | 10,714 | (135,568) | (30,483)
Less: reclassification adjustment for amortization of securities transferred from AFS to HTM, before tax | (6,781) | (5,715) | 0
Less: reclassification adjustment for amortization of securities transferred from AFS to HTM, tax | 1,458 | 1,229 | 0
Less: reclassification adjustment for amortization of securities transferred from AFS to HTM, after tax | (5,323) | (4,486) | 0
Less: reclassification adjustment for realized losses, pre-tax amount | (10,310) | (912) | 0
Less: reclassification adjustment for realized losses, tax (expense) benefit | 2,217 | 196 | 0
Less: reclassification adjustment for realized losses, after-tax amount | (8,093) | (716) | 0
Net unrealized losses, pre-tax amount | 30,737 | (166,072) | (38,832)
Net unrealized losses, tax (expense) benefit | (6,607) | 35,706 | 8,349
Net unrealized losses, after-tax amount | 24,130 | (130,366) | (30,483)
Cash Flow Hedges: |  |  |
Net increase in fair value, pre-tax amount | 179 | 10,038 | 2,987
Net increase in fair value, tax (expense) benefit | (38) | (2,158) | (642)
Net increase in fair value, after-tax amount | 141 | 7,880 | 2,345
Net increase in fair value, pre-tax amount | 261 | 9,770 | 3,627
Net increase in fair value, tax (expense) benefit | (56) | (2,100) | (780)
Net increase in fair value, after-tax amount | 205 | 7,670 | 2,847
Postretirement Plans: |  |  |
Net actuarial loss, pre-tax amount | 114 | 2,859 | (20)
Net actuarial loss, tax (expense) benefit | (25) | (614) | 4
Net actuarial loss, after-tax amount | 89 | 2,245 | (16)
Less: Amortization of net actuarial losses, pre-tax amount | 3 | (947) | (894)
Less: Amortization of net actuarial losses, tax (expense) benefit | (1) | 203 | 192
Less: Amortization of net prior service credits, after-tax amount | 2 | (744) | (702)
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 | 87 | 3,782 | 850
Net loss on postretirement plans, tax (expense) benefit | (19) | (812) | (183)
Net (loss) gain on postretirement plans, net of tax | 68 | 2,970 | 667
Other comprehensive income, pre-tax amount | 31,085 | (152,520) | (34,355)
Other comprehensive income, tax (expense) benefit | (6,682) | 32,794 | 7,386
Other comprehensive income (loss) | 24,403 | (119,726) | (26,969)
Interest Expense, Borrowings and Subordinated Debentures |  |  |
Cash Flow Hedges: |  |  |
Less: effective portion reclassified into interest expense, pre-tax amount | 3,364 | 263 | (2,254)
Less: effective portion reclassified into interest expense, tax (expense) benefit | (723) | (57) | 485
Less: effective portion reclassified into interest expense, after-tax amount | 2,641 | 206 | (1,769)
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Less: effective portion reclassified into interest expense, pre-tax amount | 3,364 | 263 | (2,254)
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax | 723 | 57 | (485)
Less: Amounts reclassified from AOCI | 2,641 | 206 | (1,769)
Interest Income, Interest and Fees on Loans |  |  |
Cash Flow Hedges: |  |  |
Less: effective portion reclassified into interest expense, pre-tax amount | (3,446) | 5 | 1,614
Less: effective portion reclassified into interest expense, tax (expense) benefit | 741 | (1) | (347)
Less: effective portion reclassified into interest expense, after-tax amount | (2,705) | 4 | 1,267
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Less: effective portion reclassified into interest expense, pre-tax amount | (3,446) | 5 | 1,614
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, Tax | (741) | 1 | 347
Less: Amounts reclassified from AOCI | $ (2,705) | $ 4 | $ 1,267

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