Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accumulated other comprehensive income (loss), before tax
Amortization of prior service costs	$ 1,443	$ 1,428
Amortization of net actuarial loss	7,320	16,106
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of year	(25,288)
Investment securities, OCI (loss)	(58,692)	(17,112)	$ 18,738
Pension and other postretirement plans, OCI	76,566	69,967	19,987
OCI	17,874	52,855	38,725
AOCI (loss), end of year	(7,414)	(25,288)
Total
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of year	(32,012)	(98,916)	(147,936)
Investment securities, OCI (loss)	(74,293)	(21,662)	23,720
Pension and other postretirement plans, OCI	96,920	88,566	25,300
OCI	22,627	66,904	49,020
AOCI (loss), end of year	(9,385)	(32,012)	(98,916)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of year	(6,724)	(20,773)	(31,068)
Investment securities, OCI (loss)	(15,601)	(4,550)	4,982
Pension and other postretirement plans, OCI	20,354	18,599	5,313
OCI	4,753	14,049	10,295
AOCI (loss), end of year	(1,971)	(6,724)	(20,773)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of year	(25,288)	(78,143)	(116,868)
Investment securities, OCI (loss)	(58,692)	(17,112)	18,738
Pension and other postretirement plans, OCI	76,566	69,967	19,987
OCI	17,874	52,855	38,725
AOCI (loss), end of year	(7,414)	(25,288)	(78,143)
Investment securities:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of year	7,722	29,384	5,664
OCI (loss) before reclassifications	(89,010)	(16,474)	22,074
Realized investment losses (gains)	14,050	(5,131)	(1,335)
Impairment losses (recoveries)	667	(57)	2,981
Investment securities, OCI (loss)	(74,293)	(21,662)	23,720
AOCI (loss), end of year	(66,571)	7,722	29,384
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of year	1,621	6,171	1,189
OCI (loss) before reclassifications	(18,692)	(3,460)	4,636
Realized investment losses (gains)	2,951	(1,078)	(280)
Impairment losses (recoveries)	140	(12)	626
Investment securities, OCI (loss)	(15,601)	(4,550)	4,982
AOCI (loss), end of year	(13,980)	1,621	6,171
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of year	6,101	23,213	4,475
OCI (loss) before reclassifications	(70,318)	(13,014)	17,438
Realized investment losses (gains)	11,099	(4,053)	(1,055)
Impairment losses (recoveries)	527	(45)	2,355
Investment securities, OCI (loss)	(58,692)	(17,112)	18,738
AOCI (loss), end of year	(52,591)	6,101	23,213
Pension and other postretirement plans:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of year	(39,734)	(128,300)	(153,600)
OCI before reclassifications	88,148	71,032	11,832
Amortization of prior service costs	1,443	1,428	1,343
Amortization of net actuarial loss	7,329	16,106	12,125
Pension and other postretirement plans, OCI	96,920	88,566	25,300
AOCI (loss), end of year	57,186	(39,734)	(128,300)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of year	(8,345)	(26,944)	(32,257)
OCI before reclassifications	18,511	14,917	2,485
Amortization of prior service costs	303	300	282
Amortization of net actuarial loss	1,540	3,382	2,546
Pension and other postretirement plans, OCI	20,354	18,599	5,313
AOCI (loss), end of year	12,009	(8,345)	(26,944)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of year	(31,389)	(101,356)	(121,343)
OCI before reclassifications	69,637	56,115	9,347
Amortization of prior service costs	1,140	1,128	1,061
Amortization of net actuarial loss	5,789	12,724	9,579
Pension and other postretirement plans, OCI	76,566	69,967	19,987
AOCI (loss), end of year	$ 45,177	$ (31,389)	$ (101,356)