Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ (33,183)
Personnel	(432,151)	$ (487,063)	$ (482,676)
Reclassification from OCI due to change in accounting principle	0	0	(84)
Interest income	3,359	895	(572)
Net other comprehensive income (loss) during period	45,801	91,789	(62,214)
Ending Balance	12,618	(33,183)
Investment Securities AFS
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	3,989	(75,643)	(38,453)
Other comprehensive income (loss) before reclassifications	55,628	111,592	(39,891)
Investment securities losses (gains), net	(9,222)	(5,957)	1,985
Personnel	0	0	0
Other Expenses	0	0
Reclassification from OCI due to change in accounting principle			(84)
Adjustment for adoption of ASU 2018-02			(8,419)
Interest income	3,359	895	(572)
Other Comprehensive Income (Loss), Tax	(12,429)	(26,898)	9,791
Net other comprehensive income (loss) during period	37,336	79,631	(37,189)
Ending Balance	41,325	3,989	(75,643)
Defined Benefit Pension and Postretirement Obligations
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(37,172)	(49,330)	(24,305)
Other comprehensive income (loss) before reclassifications	7,780	16,296	(28,612)
Investment securities losses (gains), net	0	0	0
Personnel	(148)	(148)	(148)
Other Expenses	3,897	476	2,203
Reclassification from OCI due to change in accounting principle			0
Adjustment for adoption of ASU 2018-02			(5,235)
Interest income	0	0	0
Other Comprehensive Income (Loss), Tax	(3,064)	(4,465)	6,767
Net other comprehensive income (loss) during period	8,465	12,158	(25,025)
Ending Balance	(28,707)	(37,172)	(49,330)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(33,183)	(124,972)	(62,758)
Other comprehensive income (loss) before reclassifications	63,408	127,887	(68,503)
Investment securities losses (gains), net	(9,222)	(5,957)	1,985
Personnel	(148)	(148)	(148)
Other Expenses	3,897	476	2,203
Reclassification from OCI due to change in accounting principle			(84)
Adjustment for adoption of ASU 2018-02			(13,654)
Interest income	3,359	895	(572)
Other Comprehensive Income (Loss), Tax	(15,493)	(31,363)	16,558
Net other comprehensive income (loss) during period	45,801	91,789	(62,214)
Ending Balance	$ 12,618	$ (33,183)	$ (124,972)