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Defined Benefit Pension Plans - Fair Values of Plan Investments by Asset Category (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | $ 10,206 | $ 12,665 | $ 11,890
Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 1,050 | 926 |
Insurance Fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 9,156 | 8,133 |
Securities (Assets) [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 0 | 3,606 |
Fair Value, Inputs, Level 1 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 1,050 | 926 |
Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 1,050 | 926 |
Fair Value, Inputs, Level 1 [Member] | Insurance Fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 0 | 0 |
Fair Value, Inputs, Level 1 [Member] | Securities (Assets) [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 0 | 0 |
Fair Value, Inputs, Level 3 [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 9,156 | 11,739 | 11,103
Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 0 | 0 |
Fair Value, Inputs, Level 3 [Member] | Insurance Fund [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | 9,156 | 8,133 | 8,020
Fair Value, Inputs, Level 3 [Member] | Securities (Assets) [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Total fair value of plan assets | $ 0 | $ 3,606 | $ 3,083

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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + 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 (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&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 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: 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=118257860&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(02) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 7: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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