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Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated benefit obligation |  | $ 66,800 | $ 62,300 |
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, next year |  | 9.00% |  |
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, 2018-2020 |  | 1.00% |  |
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, 2021-2022 |  | 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 |  | $ 400 | 400 | $ 300
Escrow account maintained for 2008 restricted stock plan |  | 100,000 |  |
Maximum number of shares authorized for grant |  | 300,000 |  |
Number of shares authorized for grant, unissued |  | 100,000 |  |
Fair value of vested restricted shares |  | $ 900 | $ 300 |
Middlesex [Member] | Equity Securities [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Allocation of plan assets |  | 1.40% | 2.00% |
Common stock in plan, value |  | $ 800 | $ 1,000 |
Pension Benefit Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Allocation of plan assets |  | 100.00% | 100.00% |
Benfit plan, Cash contributions |  | $ 3,600 |  |
Pension Benefit Plan [Member] | Scenario, Forecast [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benfit plan, Cash contributions | $ 3,300 |  |  |
Pension Benefit Plan [Member] | Equity Securities [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Allocation of plan assets |  | 59.70% | 59.10% |
Other Benefits Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Allocation of plan assets |  | 100.00% | 100.00% |
Benfit plan, Cash contributions |  | $ 1,600 |  |
Other Benefits Plan [Member] | Scenario, Forecast [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benfit plan, Cash contributions | $ 1,600 |  |  |
Other Benefits Plan [Member] | Equity Securities [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Allocation of plan assets |  | 54.10% | 50.00% |

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- Definition The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Health Care Cost Trend Rate -URI http://asc.fasb.org/extlink&oid=6514820 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (l) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + 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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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