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Retirement Plans (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2018 | Jun. 30, 2017 | Jun. 30, 2018 | Jun. 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 | $ 431 | $ 350 | $ 779 | $ 700
Interest Cost | 274 | 373 | 799 | 723
Expected Return on Plan Assets | (896) | (800) | (1,681) | (1,600)
Amortization of Prior Service (Credit) Cost | (13) | (14) | (25) | (28)
Amortization of Net Loss | 64 | 148 | 97 | 296
Net Periodic (Benefit) Cost | (140) | 57 | (31) | 91
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 | 196 | 10 | 207 | 20
Interest Cost | 54 | 59 | 104 | 109
Expected Return on Plan Assets | 0 | 0 | 0 | 0
Amortization of Prior Service (Credit) Cost | 15 | 14 | 29 | 28
Amortization of Net Loss | 33 | 33 | 66 | 63
Net Periodic (Benefit) Cost | 298 | 116 | 406 | 220
Plan Contributions During the Period | 117 | 116 | 233 | 229
Estimated Future Contributions in the Current Fiscal Year | 0 |  | 0 |
Post-Retirement Benefit Plans |  |  |  |
Net Periodic Benefit Cost [Line Items] |  |  |  |
Service Cost | 35 | 37 | 68 | 74
Interest Cost | 68 | 63 | 167 | 149
Expected Return on Plan Assets | 0 | 0 | 0 | 0
Amortization of Prior Service (Credit) Cost | 53 | (3) | 50 | (6)
Amortization of Net Loss | 6 | 0 | 0 | 0
Net Periodic (Benefit) Cost | 162 | 97 | 285 | 217
Plan Contributions During the Period | 102 | $ 177 | 119 | $ 230
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/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(4) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + 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/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(5) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(ii) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(iv)(01) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of contributions expected to be received by defined benefit plan from employer in next fiscal year following latest fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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