Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance			$ (33,183)				$ (33,183)
Investment securities losses (gains), net	$ 0			$ (225)			(90)	$ (13,861)
Personnel expense	(108,567)			(123,170)			(334,117)	(366,449)
Interest income	(1,296)			8			(2,628)	(279)
Total other comprehensive income (loss)	5,916	$ 15,054	16,209	22,111	$ 44,311	$ 21,597	37,178	88,020
Ending Balance	3,995						3,995
Investment Securities Available For Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	34,101		3,989	(9,773)		(75,643)	3,989	(75,643)
Other comprehensive income (loss) before reclassifications	5,840			33,173			53,900	123,139
Investment securities losses (gains), net	(7)			(3,788)			(9,222)	(5,931)
Personnel expense	0			0			0	0
Other expense	0			0			0	0
Interest income	1,296			(8)			2,628	279
Income tax (expense) benefit	(1,786)			(7,410)			(11,852)	(29,651)
Total other comprehensive income (loss)	5,342			21,967			35,454	87,836
Ending Balance	39,443	34,101		12,194	(9,773)		39,443	12,194
Defined Benefit Pension and Postretirement Obligations
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(36,021)		(37,172)	(49,290)		(49,330)	(37,172)	(49,330)
Other comprehensive income (loss) before reclassifications	0			0			0	0
Investment securities losses (gains), net	0			0			0	0
Personnel expense	(36)			(36)			(111)	(111)
Other expense	1,313			229			2,923	357
Interest income	0			0			0	0
Income tax (expense) benefit	(703)			(49)			(1,088)	(62)
Total other comprehensive income (loss)	573			144			1,724	184
Ending Balance	(35,448)	(36,021)		(49,146)	(49,290)		(35,448)	(49,146)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(1,920)		(33,183)	(59,063)		(124,972)	(33,183)	(124,972)
Other comprehensive income (loss) before reclassifications	5,840			33,173			53,900	123,139
Investment securities losses (gains), net	(7)			(3,788)			(9,222)	(5,931)
Personnel expense	(36)			(36)			(111)	(111)
Other expense	1,313			229			2,923	357
Interest income	1,296			(8)			2,628	279
Income tax (expense) benefit	(2,489)			(7,458)			(12,939)	(29,713)
Total other comprehensive income (loss)	5,916	15,054	$ 16,209	22,111	44,311	$ 21,597	37,178	88,020
Ending Balance	$ 3,995	$ (1,920)		$ (36,953)	$ (59,063)		$ 3,995	$ (36,953)