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Retirement Plans (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2018 | Sep. 30, 2017
Net Periodic Benefit Cost [Line Items] |  |  |  |
Employer matching contribution, Percentage |  |  | 5.00% |
Employees' Pension Plan |  |  |  |
Net Periodic Benefit Cost [Line Items] |  |  |  |
Service Cost | $ 389 | $ 350 | $ 1,168 | $ 1,050
Interest Cost | 400 | 362 | 1,199 | 1,085
Expected Return on Plan Assets | (841) | (800) | (2,522) | (2,399)
Amortization of Prior Service (Credit) Cost | (12) | (14) | (37) | (43)
Amortization of Net Loss | 48 | 148 | 145 | 443
Net Periodic (Benefit) Cost | (16) | 46 | (47) | 136
Plan Contributions During the Period | 0 | 0 | 0 | 0
Estimated Future Contributions in the Current Fiscal Year | 0 |  | 0 |
Select Executive Retirement Plan |  |  |  |
Net Periodic Benefit Cost [Line Items] |  |  |  |
Service Cost | 104 | 10 | 311 | 30
Interest Cost | 48 | 55 | 152 | 164
Expected Return on Plan Assets | 0 | 0 | 0 | 0
Amortization of Prior Service (Credit) Cost | 14 | 14 | 43 | 43
Amortization of Net Loss | 33 | 31 | 99 | 94
Net Periodic (Benefit) Cost | 199 | 110 | 605 | 331
Plan Contributions During the Period | 116 | 116 | 349 | 345
Estimated Future Contributions in the Current Fiscal Year | 0 |  | 0 |
Post-Retirement Benefit Plans |  |  |  |
Net Periodic Benefit Cost [Line Items] |  |  |  |
Service Cost | 34 | 37 | 102 | 110
Interest Cost | 81 | 75 | 248 | 224
Expected Return on Plan Assets | 0 | 0 | 0 | 0
Amortization of Prior Service (Credit) Cost | 25 | (3) | 75 | (8)
Amortization of Net Loss | 0 | 0 | 0 | 0
Net Periodic (Benefit) Cost | 140 | 109 | 425 | 326
Plan Contributions During the Period | 56 | $ 65 | 175 | $ 295
Estimated Future Contributions in the Current Fiscal Year | $ 0 |  | $ 0 |
On Or Subsequent to January 1, 2003 |  |  |  |
Net Periodic Benefit Cost [Line Items] |  |  |  |
Service credits, percent of eligible salaries |  |  | 6.00% |
Minimum | Prior to January 1, 2003 |  |  |  |
Net Periodic Benefit Cost [Line Items] |  |  |  |
Service credits, percent of eligible salaries |  |  | 6.00% |
Maximum | Prior to January 1, 2003 |  |  |  |
Net Periodic Benefit Cost [Line Items] |  |  |  |
Service credits, percent of eligible salaries |  |  | 12.00% |

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(5) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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