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Nonqualified Benefit Plan (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Defined Contribution Plan |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Nonqualified Defined Contribution Plan, Cost | $ 42,400,000 | $ 41,200,000 | $ 40,900,000
Nonqualified Plan | Unfunded Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Nonqualified Defined Contribution Plan, Cost | 597,000 | 736,000 | 395,000
Supplemental Employee Retirement Plan | Unfunded Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investments in nonqualified benefit plans | 121,930,000 | 122,927,000 |
Supplemental Employee Retirement Plan | Unfunded Plan [Member] | Equity Securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investments in nonqualified benefit plans | 73,838,000 | 77,388,000 |
Supplemental Employee Retirement Plan | Unfunded Plan [Member] | Life insurance carried on plan participants |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investments in nonqualified benefit plans | 37,274,000 | 38,568,000 |
Supplemental Employee Retirement Plan | Unfunded Plan [Member] | Other Investments |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Investments in nonqualified benefit plans | 10,818,000 | 6,971,000 |
Supplemental Employee Retirement Plan | Nonqualified Plan | Unfunded Plan [Member] |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Projected benefit obligation | 93,988,000 | 102,484,000 |
Accumulated benefit obligation | 93,988,000 | 102,484,000 |
Service cost | 185,000 | 289,000 | 493,000
Interest cost | 3,157,000 | 3,494,000 | 3,742,000
Amortization of prior service credit | 0 | 0 | (80,000)
Recognized net actuarial loss | 1,047,000 | 883,000 | 952,000
Curtailment gain | 0 | 0 | (3,292,000)
Net periodic benefit cost (credit) | $ 4,389,000 | $ 4,666,000 | $ 1,815,000
Benefit obligation discount rate | 3.86% | 3.20% |
Net periodic benefit cost discount rate | 3.20% | 3.56% |
Nonqualified Benefit Plan, Expected Future Benefit Payment, Next Twelve Months | $ 7,350,000 |  |
Nonqualified Benefit Plan, Expected Future Benefit Payment, Year Two | 7,766,000 |  |
Nonqualified Benefit Plan, Expected Future Benefit Payment, Year Three | 7,787,000 |  |
Nonqualified Benefit Plan, Expected Future Benefit Payment, Year Four | 7,018,000 |  |
Nonqualified Benefit Plan, Expected Future Benefit Payment, Year Five | 7,213,000 |  |
Nonqualified Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter | $ 36,885,000 |  |

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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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