Postretirement Benefit Plans (Amounts Recognized in Other Comprehensive (Loss) Income) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Postretirement Health And Life Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain), pretax	$ (22)	$ (31)
Net prior service cost, pretax	(174)	(209)
Director's Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain), pretax	67	60
Net prior service cost, pretax	$ 22	$ 43