Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2024	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2024	Jun. 30, 2023
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period		$ (13,400)			$ (13,400)
Investment securities, OCI (loss)	$ 1,541		$ (1,746)		787	$ 8,748
Pension and other postretirement plans, OCI (loss)	(3,434)		(2,742)		(4,510)	(5,484)
OCI (loss)	(1,893)	(1,830)	(4,488)	$ 7,752	(3,723)	3,264
AOCI (loss), end of period	(17,123)				(17,123)
Total
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	(19,279)	(16,963)	428	(9,385)	(16,963)	(9,385)
Investment securities, OCI (loss)	1,951		(2,210)		997	11,074
Pension and other postretirement plans, OCI (loss)	(4,347)		(3,471)		(5,709)	(6,942)
OCI (loss)	(2,396)		(5,681)		(4,712)	4,132
AOCI (loss), end of period	(21,675)	(19,279)	(5,253)	428	(21,675)	(5,253)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	(4,049)	(3,563)	90	(1,971)	(3,563)	(1,971)
Investment securities, OCI (loss)	410		(464)		210	2,326
Pension and other postretirement plans, OCI (loss)	(913)		(729)		(1,199)	(1,458)
OCI (loss)	(503)		(1,193)		(989)	868
AOCI (loss), end of period	(4,552)	(4,049)	(1,103)	90	(4,552)	(1,103)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	(15,230)	(13,400)	338	(7,414)	(13,400)	(7,414)
Investment securities, OCI (loss)	1,541		(1,746)		787	8,748
Pension and other postretirement plans, OCI (loss)	(3,434)		(2,742)		(4,510)	(5,484)
OCI (loss)	(1,893)	(1,830)	(4,488)	7,752	(3,723)	3,264
AOCI (loss), end of period	(17,123)	(15,230)	(4,150)	338	(17,123)	(4,150)
Investment securities:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	(32,356)	(31,402)	(53,287)	(66,571)	(31,402)	(66,571)
OCI (loss) before reclassifications	(627)		(4,477)		(2,181)	5,555
Realized investment losses	2,375		2,096		2,637	3,715
Impairment losses	203		171		541	1,804
Investment securities, OCI (loss)	1,951		(2,210)		997	11,074
AOCI (loss), end of period	(30,405)	(32,356)	(55,497)	(53,287)	(30,405)	(55,497)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	(6,795)	(6,595)	(11,190)	(13,980)	(6,595)	(13,980)
OCI (loss) before reclassifications	(132)		(940)		(458)	1,167
Realized investment losses	499		440		554	780
Impairment losses	43		36		114	379
Investment securities, OCI (loss)	410		(464)		210	2,326
AOCI (loss), end of period	(6,385)	(6,795)	(11,654)	(11,190)	(6,385)	(11,654)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	(25,561)	(24,807)	(42,097)	(52,591)	(24,807)	(52,591)
OCI (loss) before reclassifications	(495)		(3,537)		(1,723)	4,388
Realized investment losses	1,876		1,656		2,083	2,935
Impairment losses	160		135		427	1,425
Investment securities, OCI (loss)	1,541		(1,746)		787	8,748
AOCI (loss), end of period	(24,020)	(25,561)	(43,843)	(42,097)	(24,020)	(43,843)
Pension and other postretirement plans:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	13,077	14,439	53,715	57,186	14,439	57,186
OCI (loss) before reclassifications	(1,731)		0		(1,731)	0
Amortization of prior service costs	397		361		786	723
Amortization of net actuarial gain	(1,734)		(3,832)		(3,485)	(7,665)
Settlement gain	(1,279)		0		(1,279)	0
Pension and other postretirement plans, OCI (loss)	(4,347)		(3,471)		(5,709)	(6,942)
AOCI (loss), end of period	8,730	13,077	50,244	53,715	8,730	50,244
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	2,746	3,032	11,280	12,009	3,032	12,009
OCI (loss) before reclassifications	(364)		0		(364)	0
Amortization of prior service costs	83		76		165	152
Amortization of net actuarial gain	(364)		(805)		(732)	(1,610)
Settlement gain	(268)		0		(268)	0
Pension and other postretirement plans, OCI (loss)	(913)		(729)		(1,199)	(1,458)
AOCI (loss), end of period	1,833	2,746	10,551	11,280	1,833	10,551
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	10,331	11,407	42,435	45,177	11,407	45,177
OCI (loss) before reclassifications	(1,367)		0		(1,367)	0
Amortization of prior service costs	314		285		621	571
Amortization of net actuarial gain	(1,370)		(3,027)		(2,753)	(6,055)
Settlement gain	(1,011)		0		(1,011)	0
Pension and other postretirement plans, OCI (loss)	(3,434)		(2,742)		(4,510)	(5,484)
AOCI (loss), end of period	$ 6,897	$ 10,331	$ 39,693	$ 42,435	$ 6,897	$ 39,693