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Comprehensive Income (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance December,	$ (15,950)
Amounts reclassified into net income: Non-credit other-than-temporary impairment	68	$ 138	$ 232
Amount reclassified from AOCI, HTM	(116)	(92)	(377)
OCI before reclassifications, Defined Benefit Pension and Post Retirement Plans	(3,700)	(7,852)	1,585
Amounts reclassified from AOCI,All other	(4,537)	3,064	(9,110)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	(2,333)	(3,652)	6,185
Other comprehensive income (loss)	36,120	(6,525)	(29,213)
Balance December,	20,170	(15,950)
Accumulated Other-than-Temporary Impairment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance December,	(150)	(282)
OCI before reclassifications	23	(6)
Other comprehensive income (loss)	91	132
Balance December,	(59)	(150)	(282)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance December,	(58,072)	(54,420)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	1,367	4,200
Balance December,	(60,405)	(58,072)	(54,420)
Accumulated other comprehensive income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance December,	(15,950)	(9,425)
OCI before reclassifications	39,338	(13,835)
Amount reclassified from AOCI	(3,218)	7,310
Other comprehensive income (loss)	36,120	(6,525)	(29,213)
Balance December,	20,170	(15,950)	(9,425)
Held-to-maturity Securities [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance December,	102	194
OCI before reclassifications	0	0
Other comprehensive income (loss)	(116)	(92)
Balance December,	(14)	102	194
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance December,	42,170	45,083
OCI before reclassifications	43,015	(5,977)
Other comprehensive income (loss)	38,478	(2,913)
Balance December,	80,648	42,170	45,083
Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance December,	42,122	44,995
OCI before reclassifications	43,038	(5,983)
Amount reclassified from AOCI	(4,585)	3,110
Other comprehensive income (loss)	38,453	(2,873)
Balance December,	$ 80,575	$ 42,122	$ 44,995

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Net of tax amount of the reclassification adjustment related to held-to-maturity securities transferred from the available-for-sale category. This amount includes amortization and amounts realized from the disposal of these securities.

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