Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period			$ (7,414)				$ (7,414)
Investment securities, OCI (loss)	$ (5,902)			$ (17,178)			2,846	$ (69,082)
Pension and other postretirement plans, OCI (loss)	(2,742)			1,731			(8,226)	5,198
OCI (loss)	(8,644)	$ (4,488)	7,752	(15,447)	$ (23,248)	$ (25,189)	(5,380)	(63,884)
AOCI (loss), end of period	(12,794)						(12,794)
Investment securities:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	(55,497)		(66,571)	(57,980)		7,722	(66,571)	7,722
OCI (loss) before reclassifications	(10,064)			(26,524)			(4,509)	(96,982)
Realized investment losses	2,480			4,606			6,195	9,108
Impairment losses	113			175			1,917	429
Investment securities, OCI (loss)	(7,471)			(21,743)			3,603	(87,445)
AOCI (loss), end of period	(62,968)	(55,497)		(79,723)	(57,980)		(62,968)	(79,723)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	(11,654)		(13,980)	(12,177)		1,621	(13,980)	1,621
OCI (loss) before reclassifications	(2,114)			(5,570)			(947)	(20,366)
Realized investment losses	521			968			1,301	1,913
Impairment losses	24			37			403	90
Investment securities, OCI (loss)	(1,569)			(4,565)			757	(18,363)
AOCI (loss), end of period	(13,223)	(11,654)		(16,742)	(12,177)		(13,223)	(16,742)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	(43,843)		(52,591)	(45,803)		6,101	(52,591)	6,101
OCI (loss) before reclassifications	(7,950)			(20,954)			(3,562)	(76,616)
Realized investment losses	1,959			3,638			4,894	7,195
Impairment losses	89			138			1,514	339
Investment securities, OCI (loss)	(5,902)			(17,178)			2,846	(69,082)
AOCI (loss), end of period	(49,745)	(43,843)		(62,981)	(45,803)		(49,745)	(62,981)
Pension and other postretirement plans:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	50,244		57,186	(35,346)		(39,734)	57,186	(39,734)
Amortization of prior service costs	362			361			1,085	1,082
Amortization of net actuarial (gain) loss	(3,833)			1,830			(11,498)	5,497
Pension and other postretirement plans, OCI (loss)	(3,471)			2,191			(10,413)	6,579
AOCI (loss), end of period	46,773	50,244		(33,155)	(35,346)		46,773	(33,155)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	10,551		12,009	(7,424)		(8,345)	12,009	(8,345)
Amortization of prior service costs	76			76			228	227
Amortization of net actuarial (gain) loss	(805)			384			(2,415)	1,154
Pension and other postretirement plans, OCI (loss)	(729)			460			(2,187)	1,381
AOCI (loss), end of period	9,822	10,551		(6,964)	(7,424)		9,822	(6,964)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	39,693		45,177	(27,922)		(31,389)	45,177	(31,389)
Amortization of prior service costs	286			285			857	855
Amortization of net actuarial (gain) loss	(3,028)			1,446			(9,083)	4,343
Pension and other postretirement plans, OCI (loss)	(2,742)			1,731			(8,226)	5,198
AOCI (loss), end of period	36,951	39,693		(26,191)	(27,922)		36,951	(26,191)
Total
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	(5,253)		(9,385)	(93,326)		(32,012)	(9,385)	(32,012)
Investment securities, OCI (loss)	(7,471)			(21,743)			3,603	(87,445)
Pension and other postretirement plans, OCI (loss)	(3,471)			2,191			(10,413)	6,579
OCI (loss)	(10,942)			(19,552)			(6,810)	(80,866)
AOCI (loss), end of period	(16,195)	(5,253)		(112,878)	(93,326)		(16,195)	(112,878)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	(1,103)		(1,971)	(19,601)		(6,724)	(1,971)	(6,724)
Investment securities, OCI (loss)	(1,569)			(4,565)			757	(18,363)
Pension and other postretirement plans, OCI (loss)	(729)			460			(2,187)	1,381
OCI (loss)	(2,298)			(4,105)			(1,430)	(16,982)
AOCI (loss), end of period	(3,401)	(1,103)		(23,706)	(19,601)		(3,401)	(23,706)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	(4,150)		(7,414)	(73,725)		(25,288)	(7,414)	(25,288)
Investment securities, OCI (loss)	(5,902)			(17,178)			2,846	(69,082)
Pension and other postretirement plans, OCI (loss)	(2,742)			1,731			(8,226)	5,198
OCI (loss)	(8,644)	(4,488)	$ 7,752	(15,447)	(23,248)	$ (25,189)	(5,380)	(63,884)
AOCI (loss), end of period	$ (12,794)	$ (4,150)		$ (89,172)	$ (73,725)		$ (12,794)	$ (89,172)