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Description of Business and Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Accounting Standards Update 2017-07 [Member] |  |  |
Defined Benefit Plan, Other Cost (Credit) | $ (5,800) | $ (8,600) | $ 2,400
Minimum [Member] |  |  |
Increase in assets due to ASU 2016-02 | 150,000 |  |
Maximum [Member] |  |  |
Increase in assets due to ASU 2016-02 | $ 200,000 |  |

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