Other Comprehensive Income (Loss) - Changes in AOCI (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	$ 605,331	$ 558,393	$ 649,036	$ 668,459	$ 558,393	$ 668,459
Other Comprehensive Income (Loss) Before Reclassification	(18,330)		(92,632)		14,618	(226,223)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(30)		(62)		(32)	(356)
Total Other Comprehensive Income (Loss)	(18,360)	32,946	(92,694)	(133,885)	14,586	(226,579)
Ending Balances	602,565	605,331	574,429	649,036	602,565	574,429
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	(230,492)	(263,438)	(118,401)	15,484	(263,438)	15,484
Total Other Comprehensive Income (Loss)	(18,360)	32,946	(92,694)	(133,885)
Ending Balances	(248,852)	(230,492)	(211,095)	(118,401)	(248,852)	(211,095)
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	(229,978)	(262,924)	(117,833)	16,052	(262,924)	16,052
Other Comprehensive Income (Loss) Before Reclassification	(18,330)		(92,632)		14,618	(226,223)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(30)		(62)		(32)	(356)
Total Other Comprehensive Income (Loss)	(18,360)		(92,694)		14,586	(226,579)
Ending Balances	(248,338)	(229,978)	(210,527)	(117,833)	(248,338)	(210,527)
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	(514)	(514)	(568)	(568)	(514)	(568)
Other Comprehensive Income (Loss) Before Reclassification	0		0		0	0
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	0		0		0	0
Total Other Comprehensive Income (Loss)	0		0		0	0
Ending Balances	$ (514)	$ (514)	$ (568)	$ (568)	$ (514)	$ (568)