Other Comprehensive Income (Loss) - Changes in AOCI (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	$ 574,429	$ 649,036	$ 668,459	$ 648,997	$ 617,213	$ 624,709	$ 668,459	$ 624,709
Other Comprehensive Income (Loss) Before Reclassification	(97,945)			(14,989)			(324,168)	(22,932)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(18)			(172)			(374)	(1,179)
Total Other Comprehensive Income (Loss)	(97,963)	(92,694)	(133,885)	(15,161)	12,878	(21,828)	(324,542)	(24,111)
Ending Balances	494,701	574,429	649,036	650,139	648,997	617,213	494,701	650,139
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	(211,095)	(118,401)	15,484	26,425	13,547	35,375	15,484	35,375
Total Other Comprehensive Income (Loss)	(97,963)	(92,694)	(133,885)	(15,161)	12,878	(21,828)
Ending Balances	(309,058)	(211,095)	(118,401)	11,264	26,425	13,547	(309,058)	11,264
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	(210,527)		16,052	26,993		35,943	16,052	35,943
Other Comprehensive Income (Loss) Before Reclassification	(97,945)			(14,989)			(324,168)	(22,932)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(18)			(172)			(374)	(1,179)
Total Other Comprehensive Income (Loss)	(97,963)			(15,161)			(324,542)	(24,111)
Ending Balances	(308,490)	(210,527)		11,832	26,993		(308,490)	11,832
Postretirement Benefit Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	(568)		$ (568)	(568)		$ (568)	(568)	(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	$ (568)	$ (568)		$ (568)	$ (568)		$ (568)	$ (568)