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Employee Benefit Plans (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 USD ($) years period shares | Dec. 31, 2018 USD ($) shares | Dec. 31, 2017 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 | 57,201 | 50,750 | 38,387
Stock Issued During Period, Value, Employee Stock Purchase Plan | $ 2,100 | $ 2,000 | $ 1,500
Shares Available For Purchase Under Employee Stock Purchase Plan | shares | 303,156 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Balance at beginning of year | $ 21,287 | 20,553 |
Change in actuarial loss | 2,663 | (31) |
Benefit expense | 1,930 | 1,701 |
Defined Benefit Plan, Benefit Obligation, Benefits Paid | 966 | 936 |
Balance at end of year | $ 24,914 | 21,287 | 20,553
Pension Plan [Member] |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Requisite Service Period | 1 month |  |
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 | $ 3,500 | 3,300 | 2,700
Pension Plan [Member] | Minimum [Member] |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Eligible Age | years | 18 |  |
Pension Plan [Member] | Maximum [Member] |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Contribution Requirements, Percent Of Each Employee Compensation | 3.00% |  |
Deferred Profit Sharing [Member] |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Requisite Service Period | 1 month |  |
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 | $ 7,300 | 7,000 | 5,700
Deferred Profit Sharing [Member] | Minimum [Member] |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Eligible Age | years | 18 |  |
Deferred Profit Sharing [Member] | Maximum [Member] |  |  |
Employee Benefit [Line Items] |  |  |
Deferred Compensation Arrangement with Individual, Contribution Requirements, Percent Of Each Employee Compensation | 3.00% |  |
ESP Plan [Member] |  |  |
Employee Benefit [Line Items] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date | 90.00% |  |
Unit Plans [Member] |  |  |
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 | 4,200 |
Deferred Compensation Arrangement with Individual, Compensation Expense | $ 415 | $ 337 | $ 452
SERP [Member] |  |  |
Employee Benefit [Line Items] |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | 3.34% | 4.30% |
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] |  |  |
2020 | $ 1,971 |  |
2021 | 1,116 |  |
2022 | 1,135 |  |
2023 | 1,239 |  |
2024 | 1,438 |  |
2025 through 2029 | 8,574 |  |
Total | $ 15,473 |  |

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