Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ 12,618
Investment securities losses (gains), net	(75)	$ (80)
Personnel expense	(104,026)	(114,200)
Interest income	(518)	(556)
Total other comprehensive income (loss)	(16,811)	16,209
Ending Balance	(4,193)
Investment Securities AFS
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	41,325	3,989
Other comprehensive income (loss) before reclassifications	(23,979)	26,419
Investment securities losses (gains), net	39	(6,118)
Personnel expense	0	0
Other expense	0	0
Interest income	518	556
Income tax (expense) benefit	5,851	(5,225)
Total other comprehensive income (loss)	(17,571)	15,632
Ending Balance	23,754	19,620
Defined Benefit Pension and Postretirement Obligations
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(28,707)	(37,172)
Other comprehensive income (loss) before reclassifications	0	0
Investment securities losses (gains), net	0	0
Personnel expense	(37)	(38)
Other expense	1,050	808
Interest income	0	0
Income tax (expense) benefit	(253)	(193)
Total other comprehensive income (loss)	760	577
Ending Balance	(27,947)	(36,595)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	12,618	(33,183)
Other comprehensive income (loss) before reclassifications	(23,979)	26,419
Investment securities losses (gains), net	39	(6,118)
Personnel expense	(37)	(38)
Other expense	1,050	808
Interest income	518	556
Income tax (expense) benefit	5,598	(5,418)
Total other comprehensive income (loss)	(16,811)	16,209
Ending Balance	$ (4,193)	$ (16,974)