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Pension Plans and Other Postretirement Benefits - Components of Net Periodic Cost, Changes in Plan Assets and Benefit Obligations, and AOCI Impacts (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Amortization of: |  |  |
Total recognized in other comprehensive income (loss) | $ (1,294) | $ (1,461) | $ 37
Defined Benefit Plan |  |  |
Service cost: |  |  |
Benefit accrual | 0 | 0 | 0
Other expenses | 650 | 650 | 650
Interest cost | 947 | 1,091 | 1,244
Expected return on plan assets | (1,377) | (1,493) | (1,675)
Settlement loss | 0 | 0 | 0
Amortization of: |  |  |
Prior service cost | 0 | 0 | 0
Actuarial loss | 371 | 389 | 393
Net periodic pension expense | 591 | 637 | 612
Changes in plan assets and benefit obligations included in other comprehensive income (loss): |  |  |
Prior service cost | 0 | 0 | 0
Net actuarial loss (gain) | 177 | (1,619) | 175
Amortization of: |  |  |
Prior service cost | 0 | 0 | 0
Actuarial loss | (371) | (389) | (393)
Total recognized in other comprehensive income (loss) | $ (194) | $ (2,008) | $ (218)
Weighted average assumptions used to determine expense: |  |  |
Discount rate | 3.50% | 3.90% | 4.20%
Expected return on plan assets | 5.90% | 6.25% | 6.50%
Weighted average assumptions used to determine benefit obligations as of December 31: |  |  |
Discount rate | 4.20% | 3.50% | 3.90%
Expected return on plan assets | 5.90% | 6.25% | 6.50%
Supplemental Defined Benefit Plans |  |  |
Service cost: |  |  |
Benefit accrual | $ 0 | $ 0 | $ 0
Other expenses | 0 | 0 | 0
Interest cost | 566 | 631 | 687
Expected return on plan assets | 0 | 0 | 0
Settlement loss | 0 | 0 | 0
Amortization of: |  |  |
Prior service cost | 0 | 0 | 0
Actuarial loss | 310 | 258 | 233
Net periodic pension expense | 876 | 889 | 920
Changes in plan assets and benefit obligations included in other comprehensive income (loss): |  |  |
Prior service cost | 0 | 0 | 0
Net actuarial loss (gain) | (789) | 805 | 488
Amortization of: |  |  |
Prior service cost | 0 | 0 | 0
Actuarial loss | (310) | (258) | (233)
Total recognized in other comprehensive income (loss) | $ (1,099) | $ 547 | $ 255
Weighted average assumptions used to determine expense: |  |  |
Discount rate | 3.50% | 3.90% | 4.20%
Weighted average assumptions used to determine benefit obligations as of December 31: |  |  |
Discount rate | 4.20% | 3.50% | 3.90%

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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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