Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period		$ (7,414)			$ (7,414)
Change in unrealized holding (losses) gains on available-for-sale securities	$ (1,746)		$ (24,985)		8,748	$ (51,904)
Amortization of prior service costs and net actuarial (gain) loss on pension and other postretirement plans	(2,742)		1,737		(5,484)	3,467
OCI (loss)	(4,488)	7,752	(23,248)	$ (25,189)	3,264	(48,437)
AOCI (loss), end of period	(4,150)				(4,150)
Investment securities:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	(53,287)	(66,571)	(26,353)	7,722	(66,571)	7,722
OCI (loss) before reclassifications	(4,477)		(34,087)		5,555	(70,458)
Realized investment losses	2,096		2,422		3,715	4,502
Impairment losses	171		38		1,804	254
Investment securities, OCI (loss)	(2,210)		(31,627)		11,074	(65,702)
AOCI (loss), end of period	(55,497)	(53,287)	(57,980)	(26,353)	(55,497)	(57,980)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	(11,190)	(13,980)	(5,535)	1,621	(13,980)	1,621
OCI (loss) before reclassifications	(940)		(7,158)		1,167	(14,796)
Realized investment losses	440		508		780	945
Impairment losses	36		8		379	53
Investment securities, OCI (loss)	(464)		(6,642)		2,326	(13,798)
AOCI (loss), end of period	(11,654)	(11,190)	(12,177)	(5,535)	(11,654)	(12,177)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	(42,097)	(52,591)	(20,818)	6,101	(52,591)	6,101
OCI (loss) before reclassifications	(3,537)		(26,929)		4,388	(55,662)
Realized investment losses	1,656		1,914		2,935	3,557
Impairment losses	135		30		1,425	201
Change in unrealized holding (losses) gains on available-for-sale securities	(1,746)		(24,985)		8,748	(51,904)
AOCI (loss), end of period	(43,843)	(42,097)	(45,803)	(20,818)	(43,843)	(45,803)
Pension and other postretirement plans:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	53,715	57,186	(37,543)	(39,734)	57,186	(39,734)
Amortization of prior service costs	361		360		723	721
Amortization of net actuarial (gain) loss	(3,832)		1,837		(7,665)	3,667
Pension and other postretirement plans, OCI (loss)	(3,471)		2,197		(6,942)	4,388
AOCI (loss), end of period	50,244	53,715	(35,346)	(37,543)	50,244	(35,346)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	11,280	12,009	(7,884)	(8,345)	12,009	(8,345)
Amortization of prior service costs	76		75		152	151
Amortization of net actuarial (gain) loss	(805)		385		(1,610)	770
Pension and other postretirement plans, OCI (loss)	(729)		460		(1,458)	921
AOCI (loss), end of period	10,551	11,280	(7,424)	(7,884)	10,551	(7,424)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	42,435	45,177	(29,659)	(31,389)	45,177	(31,389)
Amortization of prior service costs	285		285		571	570
Amortization of net actuarial (gain) loss	(3,027)		1,452		(6,055)	2,897
Amortization of prior service costs and net actuarial (gain) loss on pension and other postretirement plans	(2,742)		1,737		(5,484)	3,467
AOCI (loss), end of period	39,693	42,435	(27,922)	(29,659)	39,693	(27,922)
Total
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	428	(9,385)	(63,896)	(32,012)	(9,385)	(32,012)
Investment securities, OCI (loss)	(2,210)		(31,627)		11,074	(65,702)
Pension and other postretirement plans, OCI (loss)	(3,471)		2,197		(6,942)	4,388
OCI (loss)	(5,681)		(29,430)		4,132	(61,314)
AOCI (loss), end of period	(5,253)	428	(93,326)	(63,896)	(5,253)	(93,326)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	90	(1,971)	(13,419)	(6,724)	(1,971)	(6,724)
Investment securities, OCI (loss)	(464)		(6,642)		2,326	(13,798)
Pension and other postretirement plans, OCI (loss)	(729)		460		(1,458)	921
OCI (loss)	(1,193)		(6,182)		868	(12,877)
AOCI (loss), end of period	(1,103)	90	(19,601)	(13,419)	(1,103)	(19,601)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	338	(7,414)	(50,477)	(25,288)	(7,414)	(25,288)
Change in unrealized holding (losses) gains on available-for-sale securities	(1,746)		(24,985)		8,748	(51,904)
Amortization of prior service costs and net actuarial (gain) loss on pension and other postretirement plans	(2,742)		1,737		(5,484)	3,467
OCI (loss)	(4,488)	7,752	(23,248)	(25,189)	3,264	(48,437)
AOCI (loss), end of period	$ (4,150)	$ 338	$ (73,725)	$ (50,477)	$ (4,150)	$ (73,725)