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Pension Benefits (Tables) | 12 Months Ended
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Dec. 31, 2017
Defined Benefit Plan [Abstract] |
Schedule of Net Funded Status [Table Text Block] |
| For the Years Ended December 31,
| 2017 |  | 2016
| (in thousands)
Change in benefit obligation: |  |  |
Projected benefit obligation at beginning of year | $ | 69,659 |  |  | $ | 62,547 |
Service cost | 6,638 |  |  | 8,200 |
Interest cost | 2,689 |  |  | 2,908 |
Actuarial loss | 3,708 |  |  | 2,662 |
Benefits paid | (10,757 | ) |  | (6,658 | )
Projected benefit obligation at end of year | 71,937 |  |  | 69,659 |
Change in plan assets: |  |  |
Fair value of plan assets at beginning of year | 31,731 |  |  | 25,769 |
Actual return on plan assets | 2,956 |  |  | 1,575 |
Employer contribution | 7,048 |  |  | 11,045 |
Benefits paid | (10,757 | ) |  | (6,658 | )
Fair value of plan assets at end of year | 30,978 |  |  | 31,731 |
Funded status at end of year | $ | (40,959 | ) |  | $ | (37,928 | )
Schedule of Accumulated Benefit Obligation in Excess of Fair Value of Plan Assets [Table Text Block] |
| As of December 31,
| 2017 |  | 2016
| (in thousands)
Projected benefit obligation | $ | 71,937 |  |  | $ | 69,659 |
Accumulated benefit obligation | $ | 56,045 |  |  | $ | 54,681 |
Less: Fair value of plan assets | (30,978 | ) |  | (31,731 | )
Underfunded accumulated benefit obligation | $ | 25,067 |  |  | $ | 22,950 |
Schedule of Net Periodic Pension Costs Not yet Recognized [Table Text Block] | The pre-tax amounts not yet recognized in net periodic pension costs, but rather recognized in accumulated other comprehensive loss as of December 31, 2017, and 2016, were as follows:
| As of December 31,
| 2017 |  | 2016
| (in thousands)
Unrecognized actuarial losses | $ | 21,397 |  |  | $ | 22,708 |
Unrecognized prior service costs | 66 |  |  | 83 |
Accumulated other comprehensive loss | $ | 21,463 |  |  | $ | 22,791 |
Schedule of Pension Liability Adjustments Recognized in Other Comprehensive Income (Loss) [Table Text Block] | The pension liability adjustments recognized in other comprehensive income (loss) during 2017, 2016, and 2015, were as follows:
| For the Years Ended December 31,
| 2017 |  | 2016 |  | 2015
| (in thousands)
Net actuarial loss | $ | (2,995 | ) |  | $ | (3,322 | ) |  | $ | (4,990 | )
Amortization of prior service cost | 17 |  |  | 16 |  |  | 17 |
Amortization of net actuarial loss | 1,297 |  |  | 1,582 |  |  | 1,486 |
Settlements | 3,009 |  |  | — |  |  | 350 |
Total pension liability adjustment, pre-tax | 1,328 |  |  | (1,724 | ) |  | (3,137 | )
Tax (expense) benefit | (561 | ) |  | 570 |  |  | 1,047 |
Total pension liability adjustment, net of tax | $ | 767 |  |  | $ | (1,154 | ) |  | $ | (2,090 | )
Components of Net Periodic Benefit Cost for the Pension Plans [Table Text Block] | Components of Net Periodic Benefit Cost for the Pension Plans
| For the Years Ended December 31,
| 2017 |  | 2016 |  | 2015
| (in thousands)
Components of net periodic benefit cost: |  |  |  |  |
Service cost | $ | 6,638 |  |  | $ | 8,200 |  |  | $ | 7,949 |
Interest cost | 2,689 |  |  | 2,908 |  |  | 2,496 |
Expected return on plan assets that reduces periodic pension benefit cost | (2,244 | ) |  | (2,235 | ) |  | (2,182 | )
Amortization of prior service cost | 17 |  |  | 16 |  |  | 17 |
Amortization of net actuarial loss | 1,297 |  |  | 1,582 |  |  | 1,486 |
Settlements | 3,009 |  |  | — |  |  | 350 |
Net periodic benefit cost | $ | 11,406 |  |  | $ | 10,471 |  |  | $ | 10,116 |
Schedule of Pension Plan Assumptions [Table Text Block] | The weighted-average assumptions used to measure the Company’s projected benefit obligation are as follows:
| As of December 31,
| 2017 |  | 2016
Projected benefit obligation: |  |  |
Discount rate | 3.8% |  | 4.2%
Rate of compensation increase | 6.2% |  | 6.2%
The weighted-average assumptions used to measure the Company’s net periodic benefit cost are as follows:
| For the Years Ended December 31,
| 2017 |  | 2016 |  | 2015
Net periodic benefit cost: |  |  |  |  |
Discount rate | 4.2% |  | 4.7% |  | 4.3%
Expected return on plan assets (1) | 6.5% |  | 7.5% |  | 7.5%
Rate of compensation increase | 6.2% |  | 6.2% |  | 6.2%
____________________________________________
(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.
Schedule of Weighted-Average Allocation of the Qualified Pension Plan [Table Text Block] | The weighted-average asset allocation of the Qualified Pension Plan is as follows:
|  | Target |  | As of December 31,
Asset Category |  | 2018 |  | 2017 |  | 2016
Equity securities |  | 35.0 | % |  | 38.4 | % |  | 28.8 | %
Fixed income securities |  | 43.0 | % |  | 39.8 | % |  | 35.5 | %
Other securities |  | 22.0 | % |  | 21.8 | % |  | 35.7 | %
Total |  | 100.0 | % |  | 100.0 | % |  | 100.0 | %
Schedule of Fair Values of the Qualified Plan Assets [Table Text Block] | The fair values of the Company’s Qualified Pension Plan assets as of December 31, 2017, and 2016, utilizing the fair value hierarchy discussed in Note 11 – Fair Value Measurements are as follows:
|  |  |  |  | Fair Value Measurements Using:
| Actual Asset Allocation(1) |  | Total |  | Level 1 Inputs |  | Level 2 Inputs |  | Level 3 Inputs
|  |  | (in thousands)
As of December 31, 2017 |  |  |  |  |  |  |  |  |
Cash | — | % |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Equity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Domestic (2) | 22.2 | % |  | 6,865 |  |  | 4,805 |  |  | 2,060 |  |  | — |
International (3) | 16.2 | % |  | 5,032 |  |  | 3,806 |  |  | 1,226 |  |  | — |
Total equity securities | 38.4 | % |  | 11,897 |  |  | 8,611 |  |  | 3,286 |  |  | — |
Fixed income securities: |  |  |  |  |  |  |  |  |  |  |  |  |
High-yield bonds (4) | 2.8 | % |  | 876 |  |  | 876 |  |  | — |  |  | — |
Core fixed income (5) | 28.6 | % |  | 8,842 |  |  | 8,842 |  |  | — |  |  | — |
Floating rate corp loans (6) | 8.4 | % |  | 2,607 |  |  | 2,607 |  |  | — |  |  | — |
Total fixed income securities | 39.8 | % |  | 12,325 |  |  | 12,325 |  |  | — |  |  | — |
Other securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodities (7) | 1.9 | % |  | 588 |  |  | 588 |  |  | — |  |  | — |
Real estate (8) | 5.6 | % |  | 1,735 |  |  | — |  |  | — |  |  | 1,735 |
Collective investment trusts (9) | 3.1 | % |  | 959 |  |  | — |  |  | 959 |  |  | — |
Hedge fund (10) | 11.2 | % |  | 3,474 |  |  | — |  |  | — |  |  | 3,474 |
Total other securities | 21.8 | % |  | 6,756 |  |  | 588 |  |  | 959 |  |  | 5,209 |
Total investments | 100.0 | % |  | $ | 30,978 |  |  | $ | 21,524 |  |  | $ | 4,245 |  |  | $ | 5,209 |
As of December 31, 2016 |  |  |  |  |  |  |  |  |
Cash | — | % |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Equity securities: |  |  |  |  |  |  |  |  |
Domestic (2) | 18.7 | % |  | 5,945 |  |  | 4,471 |  |  | 1,474 |  |  | — |
International (3) | 10.1 | % |  | 3,192 |  |  | 3,192 |  |  | — |  |  | — |
Total equity securities | 28.8 | % |  | 9,137 |  |  | 7,663 |  |  | 1,474 |  |  | — |
Fixed income securities: |  |  |  |  |  |  |  |  |
High-yield bonds (4) | 2.6 | % |  | 822 |  |  | 822 |  |  | — |  |  | — |
Core fixed income (5) | 25.0 | % |  | 7,923 |  |  | 7,923 |  |  | — |  |  | — |
Floating rate corp loans (6) | 7.9 | % |  | 2,495 |  |  | 2,495 |  |  | — |  |  | — |
Total fixed income securities | 35.5 | % |  | 11,240 |  |  | 11,240 |  |  | — |  |  | — |
Other securities: |  |  |  |  |  |  |  |  |
Commodities (7) | 1.8 | % |  | 578 |  |  | 578 |  |  | — |  |  | — |
Real estate (8) | 5.1 | % |  | 1,629 |  |  | — |  |  | — |  |  | 1,629 |
Collective investment trusts (9) | 17.5 | % |  | 5,562 |  |  | — |  |  | 5,562 |  |  | — |
Hedge fund (10) | 11.3 | % |  | 3,585 |  |  | — |  |  | — |  |  | 3,585 |
Total other securities | 35.7 | % |  | 11,354 |  |  | 578 |  |  | 5,562 |  |  | 5,214 |
Total investments | 100.0 | % |  | $ | 31,731 |  |  | $ | 19,481 |  |  | $ | 7,036 |  |  | $ | 5,214 |
____________________________________________
(1) | Percentages may not calculate due to rounding.
(2) | 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.
(3) | 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.
(4) | 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.
(5) | 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.
(6) | 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.
(7) | Investments with exposure to commodity price movements, primarily through the use of futures, swaps and other commodity-linked securities.
(8) | 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.
(9) | 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.
(10) | 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.
Schedule of Changes in Level 3 Plan Assets [Table Text Block] | Included below is a summary of the changes in Level 3 plan assets (in thousands):
Balance at January 1, 2016 | $ | 5,045 |
Purchases | 561 |
Realized gain on assets | 54 |
Unrealized gain on assets | 115 |
Disposition | (561 | )
Balance at December 31, 2016 | $ | 5,214 |
Purchases | 300 |
Realized gain on assets | 130 |
Unrealized gain on assets | 120 |
Disposition | (555 | )
Balance at December 31, 2017 | $ | 5,209 |
Schedule of Expected Benefit Payments [Table Text Block] | Expected benefit payments over the next 10 years are as follows:
Years Ending December 31, | (in thousands)
2018 | $ | 4,217 |
2019 | $ | 3,818 |
2020 | $ | 4,363 |
2021 | $ | 5,561 |
2022 | $ | 6,117 |
2023 through 2027 | $ | 36,279 |

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