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Employee Benefit Plans (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 USD ($) period years shares | Dec. 31, 2017 USD ($) shares | Dec. 31, 2016 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 | 50,750 | 38,387 | 50,116
Stock Issued During Period, Value, Employee Stock Purchase Plan | $ 2,000 | $ 1,500 | $ 1,800
Shares Available For Purchase Under Employee Stock Purchase Plan | shares | 360,357 |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |
Balance at beginning of year | $ 20,553 | 26,263 |
Change in actuarial loss | (31) | (6,453) |
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment | 0 | 148 |
Benefit expense | 1,701 | 1,600 |
Defined Benefit Plan, Benefit Obligation, Benefits Paid | 936 | 1,005 |
Balance at end of year | $ 21,287 | 20,553 | 26,263
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 | $ 3,300 | 2,700 | 2,400
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 | $ 7,000 | 5,700 | 5,100
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 | $ 4,200 | 4,600 |
Deferred Compensation Arrangement with Individual, Compensation Expense | $ 337 | $ 452 | $ 467
SERP [Member] |  |  |
Employee Benefit [Line Items] |  |  |
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate | 4.30% | 3.80% |
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] |  |  |
2019 | $ 963 |  |
2020 | 1,971 |  |
2021 | 2,095 |  |
2022 | 1,135 |  |
2023 | 1,236 |  |
2024 through 2028 | 8,236 |  |
Total | $ 15,636 |  |

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- Definition Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(6) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964 + Details
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