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Comprehensive Income (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance December, | $ 81,750 |  |
Amount reclassified from AOCI, HTM | (19) | $ (46) | $ 87
OCI before reclassifications, Defined Benefit Pension and Post Retirement Plans | 1,197 | (10,898) | (8,906)
Amounts reclassified from AOCI,All other | 4,247 | 530 | 31,316
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax | 3,579 | (8,799) | (7,226)
Other comprehensive income (loss) | 138,436 | 159,706 | (73,107)
Balance December, | 220,186 | 81,750 |
Accumulated Other-than-Temporary Impairment [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance December, | (71) | (71) |
Amounts reclassified into net income: Credit loss related | 3,984 | 0 |
Other comprehensive income (loss) | (2,475) | 0 |
Balance December, | (2,546) | (71) | (71)
Accumulated Net Unrealized Investment Gain (Loss) [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
OCI before reclassifications | (6,459) | 0 |
Accumulated Defined Benefit Plans Adjustment [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance, December 31, 2018 |  |  | (79,844)
Balance December, | (88,643) |  |
OCI before reclassifications, Defined Benefit Pension and Post Retirement Plans | 1,197 | (10,898) |
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax | 2,382 | 2,099 |
Balance December, | (85,064) | (88,643) |
Accumulated other comprehensive (loss) income [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance, December 31, 2018 |  |  | (77,956)
Balance December, | 81,750 |  |
OCI before reclassifications | 127,842 | 157,123 |
Amount reclassified from AOCI | 10,594 | 2,583 |
Other comprehensive income (loss) | 138,436 | 159,706 | (73,107)
Balance December, | 220,186 | 81,750 |
Held-to-maturity Securities [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance, December 31, 2018 |  |  | 71
Balance December, | 25 |  |
OCI before reclassifications | 0 | 0 |
Other comprehensive income (loss) | (19) | (46) |
Balance December, | 6 | 25 |
Available-for-sale Securities [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance, December 31, 2018 |  |  | 1,888
Balance December, | 170,439 |  |
OCI before reclassifications | 133,104 | 168,021 |
Amounts reclassified from AOCI,All other | 4,247 | 530 |
Other comprehensive income (loss) | 137,351 | 168,551 |
Balance December, | 307,790 | 170,439 |
Investments [Member] |  |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |  |
Balance, December 31, 2018 |  |  | $ 1,888
Balance December, | 170,393 |  |
OCI before reclassifications | 126,645 | 168,021 |
Amount reclassified from AOCI | 8,212 | 484 |
Other comprehensive income (loss) | 134,857 | 168,505 |
Balance December, | $ 305,250 | $ 170,393 |

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