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Benefit Plans (Fair values of our pension plan assets by asset category) (Details) - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Corporation's pension plan assets | $ 8,352 | $ 7,765 | $ 9,469
Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Corporation's pension plan assets | 8,352 | 7,765 |
Short-term investments [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Corporation's pension plan assets | 218 | 98 |
Short-term investments [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Corporation's pension plan assets | 218 | 98 |
Fixed income [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Corporation's pension plan assets | 3,823 | 2,924 |
Fixed income [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Corporation's pension plan assets | 3,823 | 2,924 |
Equity investments [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Corporation's pension plan assets | 4,311 | 4,743 |
Equity investments [Member] | Level 2 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Fair values of the Corporation's pension plan assets | $ 4,311 | $ 4,743 |

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