Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 87,600	$ 73,100
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, 2021-2022	1.00%
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, 2023-2024	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	$ 7	6	$ 6
Discretionary contributions	$ 700	600	$ 500
Number of shares authorized for grant, unissued	100,000
Fair value of vested restricted shares	$ 1,700	$ 1,300
Middlesex [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Common stock in plan, value	$ 1,200
Pension Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation of plan assets	100.00%	100.00%
Benfit plan, Cash contributions	$ 3,700
Pension Benefit Plan [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation of plan assets	61.50%	59.50%
Pension Benefit Plan [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Benfit plan, Cash contributions	$ 3,400
Other Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation of plan assets	100.00%	100.00%
Other Benefits Plan [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation of plan assets	60.00%	54.70%