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%