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Retirement Plans (Quantitative Disclosures of Retirement Income Plan's Invested Assets that are Measured at Fair Value on a Recurring Basis) (Details) - Retirement Income Plan [Member] - USD ($) $ in Thousands | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | $ 316,515 | $ 249,700 | $ 253,452
Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 316,987 | 249,781 |
Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 193,057 | 152,462 |
Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 1,832 | 1,418 |
Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Global Asset Allocation Fund [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 37,878 | 33,565 |
Global Asset Allocation Fund [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 37,878 | 33,565 |
Global Asset Allocation Fund [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Global Asset Allocation Fund [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Extended Duration Fixed Income [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 131,457 | 117,297 |
Extended Duration Fixed Income [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 131,457 | 117,297 |
Extended Duration Fixed Income [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Extended Duration Fixed Income [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Total Long Duration Fixed Income [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 169,335 | 150,862 |
Total Long Duration Fixed Income [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 169,335 | 150,862 |
Total Long Duration Fixed Income [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Total Long Duration Fixed Income [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Short-term Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 23,722 | 1,600 |
Short-term Investments [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 23,722 | 1,600 |
Short-term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Short-term Investments [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Deposit Administration Contracts [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 1,832 | 1,418 |
Deposit Administration Contracts [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Deposit Administration Contracts [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 1,832 | 1,418 |
Deposit Administration Contracts [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Cash And Short Term Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 25,554 | 3,018 |
Cash And Short Term Investments [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 23,722 | 1,600 |
Cash And Short Term Investments [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 1,832 | 1,418 |
Cash And Short Term Investments [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
International equity [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 48,836 | 42,603 |
International equity [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
International equity [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
International equity [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
US Global Equity [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 55,073 | 46,840 |
US Global Equity [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
US Global Equity [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
US Global Equity [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Global Equity [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 103,909 | 89,443 |
Global Equity [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Global Equity [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Global Equity [Member] | Significant Unobservable Inputs (Level 3) [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Real Assets [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 15,466 | 2,514 |
Real Assets [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Real Assets [Member] | Significant Other Observable Inputs (Level 2) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Real Assets [Member] | Significant Unobservable Inputs (Level 3) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Private Equity Funds [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 1,615 | 2,626 |
Private Equity Funds [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Private Equity Funds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Private Equity Funds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Private Credit Funds [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 1,108 | 1,318 |
Private Credit Funds [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Private Credit Funds [Member] | Significant Other Observable Inputs (Level 2) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Private Credit Funds [Member] | Significant Unobservable Inputs (Level 3) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 18,189 | 6,458 |
Alternative Investments [Member] | Quoted Prices in Active Markets for Identical Assets/Liabilities (Level 1) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Alternative Investments [Member] | Significant Other Observable Inputs (Level 2) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | 0 | 0 |
Alternative Investments [Member] | Significant Unobservable Inputs (Level 3) [Member] | Alternative Investments [Member] | Fair value, recurring [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total Assets | $ 0 | $ 0 |

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