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Comprehensive Income (Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2020			$ 220,186
Amounts reclassified from AOCI, HTM related	$ 1	$ 0	(3)	$ (5)
Amount reclassified into net income: Net actuarial loss	548	596	1,643	1,787
Other comprehensive income (loss)	(29,147)	35,124	(79,962)	105,340
Other comprehensive income, defined pension and post retirement plans	548	596	1,643	1,787
Ending Balance, September 30, 2021	140,224		140,224
Available-for-sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2020			307,790
OCI before reclassifications			(81,402)
Amounts reclassified from AOCI, All Other			(501)
Other comprehensive income (loss)			(81,903)
Ending Balance, September 30, 2021	225,887		225,887
Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2020			305,250
OCI before reclassifications			(84,308)
Amounts reclassified from AOCI			2,703
Other comprehensive income (loss)			(81,605)
Ending Balance, September 30, 2021	223,645		223,645
Accumulated Other-than-Temporary Impairment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2020			(2,546)
OCI before reclassifications			(2,906)
Amounts reclassified from AOCI, Credit loss related			3,207
Other comprehensive income (loss)			301
Ending Balance, September 30, 2021	(2,245)		(2,245)
Accumulated Net Unrealized Investment Gain (Loss) [Member] | Held-to-maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2020			6
OCI before reclassifications			0
Amounts reclassified from AOCI, HTM related			(3)
Other comprehensive income (loss)			(3)
Ending Balance, September 30, 2021	3		3
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2020			(85,064)
OCI before reclassifications, Defined Benefit Pension and Post Retirement Plans			0
Amount reclassified into net income: Net actuarial loss			1,643
Ending Balance, September 30, 2021	(83,421)		(83,421)
Accumulated other comprehensive income (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance, December 31, 2020			220,186
OCI before reclassifications			(84,308)
Amounts reclassified from AOCI			4,346
Other comprehensive income (loss)	(29,147)	$ 35,124	(79,962)	$ 105,340
Ending Balance, September 30, 2021	$ 140,224		$ 140,224

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