Other Comprehensive Income (Reclassifications Out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net gain on securities transactions	$ (197)	$ (11)
Income tax expense	16,226	5,257
Total reclassification	(48,559)	(14,931)
Compensation and employee benefits	35,312	31,195
Unrealized Gains (Losses) on Available for Sale Debt Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Net gain on securities transactions	230	0
Income tax expense	(59)	0
Total reclassification	171	0
Reclassification adjustment | Post-retirement obligations
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense	41	(28)
Total reclassification	(109)	84
Compensation and employee benefits	$ (150)	$ 112