Accumulated Other Comprehensive Income (Loss) (AOCI Reclass to IS) (Details 3) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	$ (50,113)	$ (50,289)	$ (101,715)	$ (100,803)
Tax Benefit (Expense)	(20,414)	(18,753)	(42,058)	(42,388)
Net Income	44,662	44,245	95,838	94,455
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(444)	(287)	(895)	(683)
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	(491)	(242)	(995)	(663)
Tax Benefit (Expense)	194	96	393	262
Net Income	(297)	(146)	(602)	(401)
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	(242)	(232)	(484)	(465)
Tax Benefit (Expense)	95	91	191	183
Net Income	(147)	(141)	(293)	(282)
Prior Service Credit | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	80	80	161	161
Net Actuarial Losses | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	$ (322)	$ (312)	$ (645)	$ (626)