Other Comprehensive Income (Loss) (Changes in AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	$ 624,709	$ 573,820
Other Comprehensive Income (Loss) Before Reclassification	(21,058)	13,718
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(770)	(463)
Total Other Comprehensive Income (Loss)	(21,828)	13,255
Ending Balances	617,213	583,540
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	35,943	15,673
Other Comprehensive Income (Loss) Before Reclassification	(21,058)	13,718
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(770)	(463)
Total Other Comprehensive Income (Loss)	(21,828)	13,255
Ending Balances	14,115	28,928
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	(568)	(568)
Other Comprehensive Income (Loss) Before Reclassification	0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0	0
Total Other Comprehensive Income (Loss)	0	0
Ending Balances	(568)	(568)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	35,375	15,105
Total Other Comprehensive Income (Loss)	(21,828)	13,255
Ending Balances	$ 13,547	$ 28,360

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.

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Amount after tax of other comprehensive income (loss) attributable to parent entity.

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