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Other Comprehensive Income (Loss) - Changes in Components of OCI (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Total other comprehensive income (loss), pre-tax | $ 32,600 | $ 25,029 | $ (9,908)
Total other comprehensive income (loss), tax expense (benefit) | 8,296 | 6,369 | (2,523)
Other comprehensive income (loss), net of tax | 24,304 | 18,660 | (7,385)
Total securities available for sale |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive income (loss), before reclassifications, pre-tax | 27,788 |  |
Other comprehensive income (loss) before reclassifications, tax expense (benefit) | 7,071 |  |
Other comprehensive income (loss), before reclassifications, net of tax | 20,717 |  |
Reclassification from AOCI, pre-tax | (46) |  |
Reclassification from AOCI, tax expense (benefit) | (12) |  |
Reclassification from AOCI, net of tax | (34) |  |
Total other comprehensive income (loss), pre-tax | 27,742 | 27,494 | (11,139)
Total other comprehensive income (loss), tax expense (benefit) | 7,059 | 6,997 | (2,836)
Other comprehensive income (loss), net of tax | 20,683 | 20,497 | (8,303)
Total derivative instruments |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive income (loss), before reclassifications, pre-tax | 923 | (2,975) | 490
Other comprehensive income (loss) before reclassifications, tax expense (benefit) | 235 | (758) | 125
Other comprehensive income (loss), before reclassifications, net of tax | 688 | (2,217) | 365
Reclassification from AOCI, pre-tax | 2,040 |  |
Reclassification from AOCI, tax expense (benefit) | 519 |  |
Reclassification from AOCI, net of tax | 1,521 |  |
Total other comprehensive income (loss), pre-tax | 2,963 | (2,975) | 490
Total other comprehensive income (loss), tax expense (benefit) | 754 | (758) | 125
Other comprehensive income (loss), net of tax | 2,209 | (2,217) | 365
Net gain arising during the period |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive income (loss), before reclassifications, pre-tax | 1,069 | 91 | 413
Other comprehensive income (loss) before reclassifications, tax expense (benefit) | 272 | 23 | 105
Other comprehensive income (loss), before reclassifications, net of tax | 797 | 68 | 308
Reclassification adjustment for settlement loss related to the VERP realized in net income |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Reclassification from AOCI, pre-tax | 567 |  |
Reclassification from AOCI, tax expense (benefit) | 145 |  |
Reclassification from AOCI, net of tax | 422 |  |
New prior service cost |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Reclassification from AOCI, pre-tax | (485) |  |
Reclassification from AOCI, tax expense (benefit) | (123) |  |
Reclassification from AOCI, net of tax | (362) |  |
Amortization of net actuarial loss recognized in net periodic pension cost |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Reclassification from AOCI, pre-tax | 259 |  |
Reclassification from AOCI, tax expense (benefit) | 66 |  |
Reclassification from AOCI, net of tax | 193 |  |
Amortization of net actuarial loss recognized in net periodic pension cost |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Reclassification from AOCI, pre-tax | 485 | 419 | 328
Reclassification from AOCI, tax expense (benefit) | 123 | 107 | 83
Reclassification from AOCI, net of tax | 362 | 312 | 245
Total defined benefit pension and post-retirement benefit plans |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Total other comprehensive income (loss), pre-tax | 1,895 | 510 | 741
Total other comprehensive income (loss), tax expense (benefit) | 483 | 130 | 188
Other comprehensive income (loss), net of tax | $ 1,412 | 380 | 553
Unrealized holding gains on securities |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Other comprehensive income (loss), before reclassifications, pre-tax |  | 24,983 | (11,155)
Other comprehensive income (loss) before reclassifications, tax expense (benefit) |  | 6,358 | (2,840)
Other comprehensive income (loss), before reclassifications, net of tax |  | 18,625 | (8,315)
Reclassification adjustment for gains realized in net income |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Reclassification from AOCI, pre-tax |  | 2,511 | 16
Reclassification from AOCI, tax expense (benefit) |  | 639 | 4
Reclassification from AOCI, net of tax |  | $ 1,872 | $ 12

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