Other Comprehensive Income (Loss) - Changes in AOCI (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	$ 668,459	$ 624,709
Other Comprehensive Income (Loss) Before Reclassification	(133,591)	(21,058)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(294)	(770)
Total Other Comprehensive Income (Loss)	(133,885)	(21,828)
Ending Balances	649,036	617,213
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	15,484	35,375
Total Other Comprehensive Income (Loss)	(133,885)	(21,828)
Ending Balances	(118,401)	13,547
Unrealized Gains and Losses on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning Balances	16,052	35,943
Other Comprehensive Income (Loss) Before Reclassification	(133,591)	(21,058)
Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)	(294)	(770)
Total Other Comprehensive Income (Loss)	(133,885)	(21,828)
Ending Balances	(117,833)	14,115
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)