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Pension Benefits Fair Value of Plan Assets in Heirarchy (Details) - USD ($) | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Return on Plan Assets | [1] | 6.50% | 7.50% | 7.50%
Defined Benefit Plan, Target Allocation Percentage of Assets |  | 100.00% |  |
Defined Benefit Plan, Asset Allocation | [2] | 100.00% | 100.00% |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 30,978,000 | $ 31,731,000 | $ 25,769,000
Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 21,524,000 | 19,481,000 |
Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 4,245,000 | 7,036,000 |
Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 5,209,000 | 5,214,000 | $ 5,045,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases |  | 300,000 | 561,000 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Realized Gain on Assets |  | 130,000 | 54,000 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Unrealized Gain on Assets |  | 120,000 | 115,000 |
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Disposition |  | $ (555,000) | $ (561,000) |
Cash [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2] | 0.00% | 0.00% |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 0 | $ 0 |
Cash [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 0 | 0 |
Cash [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 0 | 0 |
Cash [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 0 | $ 0 |
Domestic Equity Securities [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2],[3] | 22.20% | 18.70% |
Defined Benefit Plan, Fair Value of Plan Assets | [3] | $ 6,865,000 | $ 5,945,000 |
Domestic Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [3] | 4,805,000 | 4,471,000 |
Domestic Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [3] | 2,060,000 | 1,474,000 |
Domestic Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [3] | $ 0 | $ 0 |
International Equity Securities [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2],[4] | 16.20% | 10.10% |
Defined Benefit Plan, Fair Value of Plan Assets | [4] | $ 5,032,000 | $ 3,192,000 |
International Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [4] | 3,806,000 | 3,192,000 |
International Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [4] | 1,226,000 | 0 |
International Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [4] | $ 0 | $ 0 |
Equity Securities [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Target Allocation Percentage of Assets |  | 35.00% |  |
Defined Benefit Plan, Asset Allocation | [2] | 38.40% | 28.80% |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 11,897,000 | $ 9,137,000 |
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 8,611,000 | 7,663,000 |
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 3,286,000 | 1,474,000 |
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 0 | $ 0 |
High-yield Bonds [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2],[5] | 2.80% | 2.60% |
Defined Benefit Plan, Fair Value of Plan Assets | [5] | $ 876,000 | $ 822,000 |
High-yield Bonds [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [5] | 876,000 | 822,000 |
High-yield Bonds [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [5] | 0 | 0 |
High-yield Bonds [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [5] | $ 0 | $ 0 |
Fixed Income Investments [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2],[6] | 28.60% | 25.00% |
Defined Benefit Plan, Fair Value of Plan Assets | [6] | $ 8,842,000 | $ 7,923,000 |
Fixed Income Investments [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [6] | 8,842,000 | 7,923,000 |
Fixed Income Investments [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [6] | 0 | 0 |
Fixed Income Investments [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [6] | $ 0 | $ 0 |
Floating Rate Corporate Loans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2],[7] | 8.40% | 7.90% |
Defined Benefit Plan, Fair Value of Plan Assets | [7] | $ 2,607,000 | $ 2,495,000 |
Floating Rate Corporate Loans [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [7] | 2,607,000 | 2,495,000 |
Floating Rate Corporate Loans [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [7] | 0 | 0 |
Floating Rate Corporate Loans [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [7] | $ 0 | $ 0 |
Fixed Income Securities [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Target Allocation Percentage of Assets |  | 43.00% |  |
Defined Benefit Plan, Asset Allocation | [2] | 39.80% | 35.50% |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 12,325,000 | $ 11,240,000 |
Fixed Income Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 12,325,000 | 11,240,000 |
Fixed Income Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 0 | 0 |
Fixed Income Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 0 | $ 0 |
Commodity Contracts [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2],[8] | 1.90% | 1.80% |
Defined Benefit Plan, Fair Value of Plan Assets | [8] | $ 588,000 | $ 578,000 |
Commodity Contracts [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [8] | 588,000 | 578,000 |
Commodity Contracts [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [8] | 0 | 0 |
Commodity Contracts [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [8] | $ 0 | $ 0 |
Real Estate [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2],[9] | 5.60% | 5.10% |
Defined Benefit Plan, Fair Value of Plan Assets | [9] | $ 1,735,000 | $ 1,629,000 |
Real Estate [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [9] | 0 | 0 |
Real Estate [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [9] | 0 | 0 |
Real Estate [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [9] | $ 1,735,000 | $ 1,629,000 |
Collective Investment Trusts [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2],[10] | 3.10% | 17.50% |
Defined Benefit Plan, Fair Value of Plan Assets | [10] | $ 959,000 | $ 5,562,000 |
Collective Investment Trusts [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [10] | 0 | 0 |
Collective Investment Trusts [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [10] | 959,000 | 5,562,000 |
Collective Investment Trusts [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [10] | $ 0 | $ 0 |
Hedge Fund [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Asset Allocation | [2],[11] | 11.20% | 11.30% |
Defined Benefit Plan, Fair Value of Plan Assets | [11] | $ 3,474,000 | $ 3,585,000 |
Hedge Fund [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [11] | 0 | 0 |
Hedge Fund [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [11] | 0 | 0 |
Hedge Fund [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets | [11] | $ 3,474,000 | $ 3,585,000 |
Other Securities [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Target Allocation Percentage of Assets |  | 22.00% |  |
Defined Benefit Plan, Asset Allocation | [2] | 21.80% | 35.70% |
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 6,756,000 | $ 11,354,000 |
Other Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 588,000 | 578,000 |
Other Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 959,000 | 5,562,000 |
Other Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Fair Value of Plan Assets |  | 5,209,000 | $ 5,214,000 |
Nonqualified Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Return on Plan Assets |  |  | 0.00% | 0.00%
Defined Benefit Plan, Fair Value of Plan Assets |  | $ 0 | $ 0 | $ 0
[1] | There is no assumed expected return on plan assets for the Nonqualified Pension Plan because there are no plan assets in the Nonqualified Pension Plan.
[2] | Percentages may not calculate due to rounding.
[3] | Level 1 equity securities consist of United States large and small capitalization companies, which are actively traded securities that can be sold upon demand. Level 2 equity securities are investments in a collective investment fund that is valued at net asset value based on the value of the underlying investments and total units outstanding on a daily basis. The objective of this fund is to approximate the S&P 500 by investing in one or more collective investment funds.
[4] | International equity securities consists of a well-diversified portfolio of holdings of mostly large issuers organized in developed countries with liquid markets, commingled with investments in equity securities of issuers located in emerging markets and believed to have strong sustainable financial productivity at attractive valuations.
[5] | High-yield bonds consist of non-investment grade fixed income securities. The investment objective is to obtain high current income. Due to the increased level of default risk, security selection focuses on credit-risk analysis.
[6] | The objective of core fixed income funds is to achieve value added from sector or issue selection by constructing a portfolio to approximate the investment results of the Barclay’s Capital Aggregate Bond Index with a modest amount of variability in duration around the index.
[7] | Investments consist of floating rate bank loans. The interest rates on these loans are typically reset on a periodic basis to account for changes in the level of interest rates.
[8] | Investments with exposure to commodity price movements, primarily through the use of futures, swaps and other commodity-linked securities.
[9] | The investment objective of direct real estate is to provide current income with the potential for long-term capital appreciation. Ownership in real estate entails a long-term time horizon, periodic valuations, and potentially low liquidity.
[10] | Collective investment trusts invest in short-term investments and are valued at the net asset value of the collective investment trust. The net asset value, as provided by the trustee, is used as a practical expedient to estimate fair value. The net asset value is based on the fair value of the underlying investments held by the fund less its liabilities.
[11] | The hedge fund portfolio includes an investment in an actively traded global mutual fund that focuses on alternative investments and a hedge fund of funds that invests both long and short using a variety of investment strategies.

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