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Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated benefit obligation		$ 75,700	$ 66,800
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, 2019-2021		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		$ 500	400	$ 400
Escrow account maintained for 2008 restricted stock plan		100
Maximum number of shares authorized for grant		300,000
Number of shares authorized for grant, unissued		50,000
Fair value of vested restricted shares		$ 800	$ 900
Middlesex [Member] | Equity Securities [Member]
Allocation of plan assets		1.10%	1.40%
Common stock in plan, value		$ 800	$ 800
Pension Benefit Plan [Member]
Allocation of plan assets		100.00%	100.00%
Benfit plan, Cash contributions		$ 3,600
Pension Benefit Plan [Member] | Equity Securities [Member]
Allocation of plan assets		62.80%	59.70%
Pension Benefit Plan [Member] | Scenario, Forecast [Member]
Benfit plan, Cash contributions	$ 3,300
Other Benefits Plan [Member]
Allocation of plan assets		100.00%	100.00%
Benfit plan, Cash contributions		$ 1,600
Other Benefits Plan [Member] | Equity Securities [Member]
Allocation of plan assets		57.70%	54.10%
Other Benefits Plan [Member] | Scenario, Forecast [Member]
Benfit plan, Cash contributions	$ 1,600

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The value of equity securities with the plan.

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Escrow account maintained for 2008 restricted stock plan

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Increase (decrease) in annual rate per capita cost of covered healthcare benefits, years four and five.

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Increase (decrease) in annual rate per capita cost of covered healthcare benefits,years one to three

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Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
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Amount of accumulated benefit obligation for defined benefit pension plan with accumulated benefit obligation in excess of plan assets.

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Ultimate trend rate for health care cost for defined benefit postretirement plan.

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Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

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Amount of discretionary contributions made by an employer to a defined contribution plan.

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Amount of payment for pension and other postretirement benefits.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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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).

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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