Employee Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 101.7	$ 87.6
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, next year	7.50%
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, 2022-2027	0.50%
Increase (decrease) in annual rate per capita cost of covered healthcare benefits, 2027	4.50%
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	$ 0.7	0.7	$ 0.6
Discretionary contributions, percent	5.00%
Discretionary contributions	$ 0.7	0.7	$ 0.6
Maximum number of shares authorized for grant	300,000
Fair value of vested restricted shares	$ 1.7	$ 1.7
Middlesex [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation of plan assets	1.60%	1.60%
Common stock in plan, value	$ 1.4	$ 1.2
Pension Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation of plan assets	100.00%	100.00%
Benfit plan, Cash contributions	$ 3.4
Pension Benefit Plan [Member] | Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Allocation of plan assets	60.60%	61.50%
Pension Benefit Plan [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Benfit plan, Cash contributions		$ 3.4
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	62.30%	60.00%
Other Benefits Plan [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Benfit plan, Cash contributions	$ 0.8	$ 1.1