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Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Accumulated benefit obligation |  | $ 73,100 | $ 75,700 |
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, next year |  | 8.00% |  |
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, 2020-2021 |  | 1.00% |  |
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, 2022-2023 |  | 0.50% |  |
Annual rate of increase in the per capita cost of covered healthcare benefits |  | 5.00% |  |
Number of hours required to participate in contribution plan |  | 1,000 |  |
Percent of participants contributions matched by company, below one percent of participants compensation |  | 100.00% |  |
Percent of participants contributions matched by company, above one percent of participants compensation |  | 50.00% |  |
Threshold percentage of participants compensation at which matching decreases |  | 1.00% |  |
Matching contributions, percent |  | 6.00% |  |
Matching contributions |  | $ 600 | 600 | $ 600
Discretionary contributions, percent |  | 5.00% |  |
Discretionary contributions |  | $ 600 | 500 | $ 400
Maximum number of shares authorized for grant |  | 300,000 |  |
Number of shares authorized for grant, unissued |  | 50,000 |  |
Fair value of vested restricted shares |  | $ 1,300 | $ 800 |
Middlesex [Member] | Equity Securities [Member] |  |  |  |
Allocation of plan assets |  | 1.60% | 1.10% |
Common stock in plan, value |  | $ 1,000 | $ 800 |
Pension Benefit Plan [Member] |  |  |  |
Allocation of plan assets |  | 1.00% | 100.00% |
Benfit plan, Cash contributions |  | $ 3,600 |  |
Pension Benefit Plan [Member] | Equity Securities [Member] |  |  |  |
Allocation of plan assets |  | 59.50% | 62.80% |
Pension Benefit Plan [Member] | Scenario, Forecast [Member] |  |  |  |
Benfit plan, Cash contributions | $ 3,600 |  |  |
Other Benefits Plan [Member] |  |  |  |
Allocation of plan assets |  | 1.00% | 100.00% |
Benfit plan, Cash contributions |  | $ 1,400 |  |
Other Benefits Plan [Member] | Equity Securities [Member] |  |  |  |
Allocation of plan assets |  | 54.70% | 57.70% |
Other Benefits Plan [Member] | Scenario, Forecast [Member] |  |  |  |
Benfit plan, Cash contributions | $ 1,400 |  |  |

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- Definition Percentage employer discretionary contribution to a defined contribution plan. + References No definition available. + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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