Accumulated Other Comprehensive Income - Unrealized gains (losses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (141,250)	$ (126,630)	$ (139,974)	$ (2,426)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(34,788)	(40,745)	(36,064)	(164,949)
Ending balance	(176,038)	(167,375)	(176,038)	(167,375)
Unrealized gains and (Losses) on available- for-sale Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(130,466)	(109,159)	(128,896)	15,674
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(34,934)	(41,060)	(36,504)	(165,893)
Ending balance	(165,400)	(150,219)	(165,400)	(150,219)
Unrealized gains (losses) on securities available-for-sale without other than temporary impairment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(132,671)	(111,474)	(131,135)	13,155
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	(34,997)	(41,078)	(36,533)	(165,707)
Ending balance	(167,668)	(152,552)	(167,668)	(152,552)
Unrealized gains (losses) on securities available-for-sale with other than temporary impairment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	2,205	2,315	2,239	2,519
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	63	18	29	(186)
Ending balance	2,268	2,333	2,268	2,333
Retirement plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(10,784)	(17,471)	(11,078)	(18,100)
Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent	146	315	440	944
Ending balance	$ (10,638)	$ (17,156)	$ (10,638)	$ (17,156)