Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ 12,618				$ 12,618
Investment securities losses (gains), net	$ 0			$ 0			(437)	$ (90)
Personnel expense	(107,880)			(108,567)			(318,900)	(334,117)
Interest income	(172)			(1,296)			(1,335)	(2,628)
Other comprehensive income (loss)	(13,702)	$ 7,082	(16,811)	5,916	$ 15,054	$ 16,209	(23,431)	37,178
Ending Balance	(10,813)						(10,813)
Investment Securities AFS
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	30,076		41,325	34,101		3,989	41,325	3,989
Other comprehensive income (loss) before reclassifications	(19,827)			5,840			(35,829)	53,900
Investment securities losses (gains), net	0			(7)			16	(9,222)
Personnel expense	0			0			0	0
Other expense	0			0			0	0
Interest income	172			1,296			1,335	2,628
Income tax (expense) benefit	4,975			(1,786)			8,548	(11,852)
Other comprehensive income (loss)	(14,681)			5,342			(25,930)	35,454
Ending Balance	15,395	30,076		39,443	34,101		15,395	39,443
Defined Benefit Pension and Postretirement Obligations
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(27,187)		(28,707)	(36,021)		(37,172)	(28,707)	(37,172)
Other comprehensive income (loss) before reclassifications	0			0			0	0
Investment securities losses (gains), net	0			0			0	0
Personnel expense	(37)			(36)			(111)	(111)
Other expense	1,346			1,313			3,446	2,923
Interest income	0			0			0	0
Income tax (expense) benefit	(330)			(703)			(836)	(1,088)
Other comprehensive income (loss)	979			573			2,498	1,724
Ending Balance	(26,209)	(27,187)		(35,448)	(36,021)		(26,209)	(35,448)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	2,889		12,618	(1,920)		(33,183)	12,618	(33,183)
Other comprehensive income (loss) before reclassifications	(19,827)			5,840			(35,829)	53,900
Investment securities losses (gains), net	0			(7)			16	(9,222)
Personnel expense	(37)			(36)			(111)	(111)
Other expense	1,346			1,313			3,446	2,923
Interest income	172			1,296			1,335	2,628
Income tax (expense) benefit	4,644			(2,489)			7,712	(12,939)
Other comprehensive income (loss)	(13,702)	7,082	$ (16,811)	5,916	15,054	$ 16,209	(23,431)	37,178
Ending Balance	$ (10,813)	$ 2,889		$ 3,995	$ (1,920)		$ (10,813)	$ 3,995