Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period			$ (13,400)				$ (13,400)
Investment securities, OCI (loss)	$ 20,227			$ (5,902)			21,014	$ 2,846
Pension and other postretirement plans, OCI (loss)	(1,538)			(2,742)			(6,048)	(8,226)
OCI (loss)	18,689	$ (1,893)	(1,830)	(8,644)	$ (4,488)	$ 7,752	14,966	(5,380)
AOCI (loss), end of period	1,566						1,566
Total
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	(21,675)		(16,963)	(5,253)		(9,385)	(16,963)	(9,385)
Investment securities, OCI (loss)	25,603			(7,471)			26,600	3,603
Pension and other postretirement plans, OCI (loss)	(1,947)			(3,471)			(7,656)	(10,413)
OCI (loss)	23,656			(10,942)			18,944	(6,810)
AOCI (loss), end of period	1,981	(21,675)		(16,195)	(5,253)		1,981	(16,195)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	(4,552)		(3,563)	(1,103)		(1,971)	(3,563)	(1,971)
Investment securities, OCI (loss)	5,376			(1,569)			5,586	757
Pension and other postretirement plans, OCI (loss)	(409)			(729)			(1,608)	(2,187)
OCI (loss)	4,967			(2,298)			3,978	(1,430)
AOCI (loss), end of period	415	(4,552)		(3,401)	(1,103)		415	(3,401)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	(17,123)		(13,400)	(4,150)		(7,414)	(13,400)	(7,414)
Investment securities, OCI (loss)	20,227			(5,902)			21,014	2,846
Pension and other postretirement plans, OCI (loss)	(1,538)			(2,742)			(6,048)	(8,226)
OCI (loss)	18,689	(1,893)	(1,830)	(8,644)	(4,488)	7,752	14,966	(5,380)
AOCI (loss), end of period	1,566	(17,123)		(12,794)	(4,150)		1,566	(12,794)
Investment securities:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	(30,405)		(31,402)	(55,497)		(66,571)	(31,402)	(66,571)
OCI (loss) before reclassifications	25,586			(10,064)			23,405	(4,509)
Realized investment (gains) losses	(142)			2,480			2,495	6,195
Impairment losses	159			113			700	1,917
Investment securities, OCI (loss)	25,603			(7,471)			26,600	3,603
AOCI (loss), end of period	(4,802)	(30,405)		(62,968)	(55,497)		(4,802)	(62,968)
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	(6,385)		(6,595)	(11,654)		(13,980)	(6,595)	(13,980)
OCI (loss) before reclassifications	5,373			(2,114)			4,915	(947)
Realized investment (gains) losses	(30)			521			524	1,301
Impairment losses	33			24			147	403
Investment securities, OCI (loss)	5,376			(1,569)			5,586	757
AOCI (loss), end of period	(1,009)	(6,385)		(13,223)	(11,654)		(1,009)	(13,223)
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	(24,020)		(24,807)	(43,843)		(52,591)	(24,807)	(52,591)
OCI (loss) before reclassifications	20,213			(7,950)			18,490	(3,562)
Realized investment (gains) losses	(112)			1,959			1,971	4,894
Impairment losses	126			89			553	1,514
Investment securities, OCI (loss)	20,227			(5,902)			21,014	2,846
AOCI (loss), end of period	(3,793)	(24,020)		(49,745)	(43,843)		(3,793)	(49,745)
Pension and other postretirement plans:
Accumulated other comprehensive income (loss), before tax
AOCI (loss), beginning of period	8,730		14,439	50,244		57,186	14,439	57,186
OCI (loss) before reclassifications	(606)			0			(2,337)	0
Amortization of prior service costs	413			362			1,199	1,085
Amortization of net actuarial gain	(1,695)			(3,833)			(5,180)	(11,498)
Settlement gain	(59)			0			(1,338)	0
Pension and other postretirement plans, OCI (loss)	(1,947)			(3,471)			(7,656)	(10,413)
AOCI (loss), end of period	6,783	8,730		46,773	50,244		6,783	46,773
Accumulated other comprehensive income (loss), tax
AOCI (loss), beginning of period	1,833		3,032	10,551		12,009	3,032	12,009
OCI (loss) before reclassifications	(127)			0			(491)	0
Amortization of prior service costs	87			76			252	228
Amortization of net actuarial gain	(356)			(805)			(1,088)	(2,415)
Settlement gain	(13)			0			(281)	0
Pension and other postretirement plans, OCI (loss)	(409)			(729)			(1,608)	(2,187)
AOCI (loss), end of period	1,424	1,833		9,822	10,551		1,424	9,822
Accumulated other comprehensive income (loss), net of tax
AOCI (loss), beginning of period	6,897		$ 11,407	39,693		$ 45,177	11,407	45,177
OCI (loss) before reclassifications	(479)			0			(1,846)	0
Amortization of prior service costs	326			286			947	857
Amortization of net actuarial gain	(1,339)			(3,028)			(4,092)	(9,083)
Settlement gain	(46)			0			(1,057)	0
Pension and other postretirement plans, OCI (loss)	(1,538)			(2,742)			(6,048)	(8,226)
AOCI (loss), end of period	$ 5,359	$ 6,897		$ 36,951	$ 39,693		$ 5,359	$ 36,951