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Employee and Retiree Benefit Plans (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Supplemental Executive Retirement Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Liability for retirement plan | $ 3.7 | $ 2.1 |
Profit Sharing Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Profit sharing contributions | $ 1.8 | 1.5 | $ (0.8)
Thrift Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Company matching contribution (percent) | 100.00% |  |
Employee's maximum contribution matched by Company (percent) | 6.00% |  |
Profit sharing percentage 1 | 5.00% |  |
Profit sharing percentage 2 | 7.00% |  |
Profit sharing percentage 3 | 9.00% |  |
Profit sharing contributions | $ 15.3 | $ 12.9 | $ 9.7

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