Retirement Plans (Changes in Accumulated Other Comprehensive Income (Loss) Related to Retirement Plans) (Details) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)
Pension Plan
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	$ (20,483)
Net actuarial income (loss)	(9,032)
Comprehensive income (loss) adjustment	(9,032)
Accumulated other comprehensive income (loss) at end of year	(29,515)
Postretirement Plan
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	744
Net actuarial income (loss)	51
Comprehensive income (loss) adjustment	51
Accumulated other comprehensive income (loss) at end of year	795
SERP
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	(69)
Net actuarial income (loss)	23
Comprehensive income (loss) adjustment	23
Accumulated other comprehensive income (loss) at end of year	(46)
Defined Benefit Pension Plans
Accumulated Other Comprehensive Income (Loss), Net of Tax
Accumulated other comprehensive income (loss) at beginning of year	(19,808)
Net actuarial income (loss)	(8,958)
Comprehensive income (loss) adjustment	(8,958)
Accumulated other comprehensive income (loss) at end of year	$ (28,766)

Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax [Roll Forward]

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Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, after tax and reclassification adjustment, of (increase) decrease in accumulated other comprehensive income for defined benefit plan.

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Amount, after tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

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