Accumulated Other Comprehensive Income (Loss) (AOCI Reclass to IS) (Details 3) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	$ (54,345)			$ (51,782)			$ (164,442)	$ (158,352)
Tax Benefit (Expense)	(14,752)			(13,138)			(44,315)	(36,365)
Net Income	52,052	$ 56,919	$ 58,799	56,933	$ 54,718	$ 54,040	167,770	165,691
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(274)			(566)			(1,282)	(1,907)
Amortization of Unrealized Gains(Losses) of Investment Securities Transferred from AFS to HTM | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Income	(39)			(476)			(804)	(1,712)
Tax Benefit (Expense)	10			126			212	453
Net Income	(29)			(350)			(592)	(1,259)
Sale of Investment Securities Available-for-Sale [Member] | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Tax Benefit (Expense)							(17)	0
Net Income							46	0
Available-for-sale Securities, Gross Realized Gain (Loss)							63	0
Amortization of Defined Benefit Pension Items | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	(334)			(295)			(1,002)	(883)
Tax Benefit (Expense)	89			79			266	235
Net Income	(245)			(216)			(736)	(648)
Prior Service Credit | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	72			142			216	426
Net Actuarial Losses | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	$ (406)			$ (437)			$ (1,218)	$ (1,309)