Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance		$ (33,183)			$ (33,183)
Investment securities losses (gains), net	$ (11)		$ (13,636)		(90)	$ (13,636)
Personnel expense	(111,350)		(123,228)		(225,551)	(243,279)
Interest income	(776)		(218)		(1,332)	(288)
Total other comprehensive income (loss)	15,054	16,209	44,311	$ 21,597	31,263	65,909
Ending Balance	(1,920)				(1,920)
Investment Securities Available For Sale
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	19,620	3,989	(54,065)	(75,643)	3,989	(75,643)
Other comprehensive income (loss) before reclassifications	21,641		59,476		48,060	89,966
Investment securities losses (gains), net	(3,096)		(463)		(9,214)	(2,143)
Personnel expense	0		0		0	0
Other expense	0		0		0	0
Interest income	776		218		1,332	288
Income tax (expense) benefit	(4,841)		(14,940)		(10,066)	(22,242)
Total other comprehensive income (loss)	14,481		44,292		30,112	65,869
Ending Balance	34,101	19,620	(9,773)	(54,065)	34,101	(9,773)
Defined Benefit Pension and Postretirement Obligations
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(36,595)	(37,172)	(49,310)	(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	(38)		(38)		(75)	(75)
Other expense	803		64		1,610	128
Interest income	0		0		0	0
Income tax (expense) benefit	(192)		(7)		(385)	(13)
Total other comprehensive income (loss)	573		20		1,150	40
Ending Balance	(36,021)	(36,595)	(49,290)	(49,310)	(36,021)	(49,290)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(16,974)	(33,183)	(103,375)	(124,972)	(33,183)	(124,972)
Other comprehensive income (loss) before reclassifications	21,641		59,476		48,060	89,966
Investment securities losses (gains), net	(3,096)		(463)		(9,214)	(2,143)
Personnel expense	(38)		(38)		(75)	(75)
Other expense	803		64		1,610	128
Interest income	776		218		1,332	288
Income tax (expense) benefit	(5,032)		(14,947)		(10,450)	(22,255)
Total other comprehensive income (loss)	15,054	16,209	44,311	21,597	31,263	65,909
Ending Balance	$ (1,920)	$ (16,974)	$ (59,063)	$ (103,375)	$ (1,920)	$ (59,063)