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Employee Benefit Plans (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 USD ($) years period shares | Dec. 31, 2019 USD ($) shares | Dec. 31, 2018 USD ($) shares
Employee Benefit [Line Items] |  |  |
Number of Look-back Period Under Employee Stock Purchase Plan | period | 2 |  |
Look-back Period Under Employee Stock Purchase Plan | 6 months |  |
Discount On Common Stock Under Employee Stock Purchase Plan, Percent | 10.00% |  |
Stock Issued During Period, Shares, Employee Stock Purchase Plans | shares | 79,297 | 57,201 | 50,750
Stock Issued During Period, Value, Employee Stock Purchase Plan | $ 2,200 | $ 2,100 | $ 2,000
Shares Available For Purchase Under Employee Stock Purchase Plan | shares | 223,859 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Balance at beginning of year | $ 24,914 | 21,287 |
Change in actuarial loss | 2,836 | 2,663 |
Benefit expense | 1,887 | 1,930 |
Defined Benefit Plan, Benefit Obligation, Benefits Paid | 2,235 | 966 |
Balance at end of year | 27,402 | 24,914 | 21,287
Pension Plan |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Contributions by Employer | $ 3,800 | 3,500 | 3,300
Pension Plan | Minimum |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Eligible Age | years | 18 |  |
Pension Plan | Maximum |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Contribution Requirements, Percent Of Each Employee Compensation | 3.00% |  |
Deferred Profit Sharing |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Contribution To Plan By Employee, Percent Of Eligible Compensation | 75.00% |  |
Deferred Compensation Arrangement with Individual, Contribution Requirements, Matching Percent | 50.00% |  |
Deferred Compensation Arrangement with Individual, Contributions by Employer | $ 8,100 | 7,300 | 7,000
Deferred Profit Sharing | Minimum |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Eligible Age | years | 18 |  |
Deferred Profit Sharing | Maximum |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Contribution Requirements, Percent Of Each Employee Compensation | 3.00% |  |
ESP Plan |  |  |
Employee Benefit [Line Items] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date | 90.00% |  |
Unit Plans |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Vesting Period | 10 |  |
Deferred Compensation Arrangement with Individual, Benefit Period | 10 |  |
Deferred Compensation Arrangement with Individual, Recorded Liability | $ 4,000 | 4,000 |
Deferred Compensation Arrangement with Individual, Compensation Expense | $ 488 | $ 415 | $ 337
SERP |  |  |
Employee Benefit [Line Items] |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | 2.51% | 3.34% |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Normal Retirement Age | years | 65 |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Annual Cost Of Living Benefit Adjustment | 2.00% |  |
Defined Benefit Plan, Expected Future Benefit Payment [Abstract] |  |  |
2021 | $ 1,111 |  |
2022 | 1,117 |  |
2023 | 1,203 |  |
2024 | 1,520 |  |
2025 | 1,717 |  |
2026 through 2030 | 7,784 |  |
Total | $ 14,452 |  |

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