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Benefit Plans (Details) - USD ($) $ in Thousands | 1 Months Ended | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
Jul. 31, 2021 | Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020
Pension and Supplemental Executive Retirement Plans |  |  |  |  |
Components of Net Periodic Benefit Cost [Abstract] |  |  |  |  |
Service cost |  | $ 2,152 | $ 1,876 | $ 3,816 | $ 3,697
Interest cost |  | 2,779 | 3,336 | 5,589 | 6,750
Expected return on plan assets |  | (5,256) | (5,473) | (10,458) | (11,053)
Amortization of net actuarial losses (gains) |  | 1,255 | 1,526 | 2,805 | 3,160
Amortization of prior service cost (credit) |  | (59) | (62) | (119) | (124)
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total |  | 871 | 1,203 | 1,633 | 2,430
Other Postretirement Benefit Plans |  |  |  |  |
Components of Net Periodic Benefit Cost [Abstract] |  |  |  |  |
Service cost |  | 390 | 322 | 754 | 631
Interest cost |  | 160 | 202 | 324 | 416
Expected return on plan assets |  | (2,216) | (1,852) | (4,431) | (3,704)
Amortization of net actuarial losses (gains) |  | (409) | (201) | (848) | (391)
Amortization of prior service cost (credit) |  | 53 | 12 | 106 | 25
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Total |  | $ (2,022) | $ (1,517) | $ (4,095) | $ (3,023)
Pension Plan | Subsequent Event |  |  |  |  |
Components of Net Periodic Benefit Cost [Abstract] |  |  |  |  |
Company contribution to pension plan | $ 6,800 |  |  |  |

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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/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921 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=123447040&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 (b) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920 Reference 4: 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=123447040&loc=d3e1928-114920 Reference 5: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4587-114921 Reference 6: 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=123447040&loc=d3e1928-114920 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=123447040&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/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=123450688&loc=d3e4587-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(3) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 3A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123453770&loc=SL108413299-114919 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920 + Details
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