Accumulated Other Comprehensive Income (Loss) (AOCI Reclass to IS) (Details 3) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	$ (51,626)	$ (49,725)	$ (153,341)	$ (150,528)
Tax Benefit (Expense)	(20,248)	(18,501)	(62,306)	(60,889)
Net Income	45,881	43,493	141,719	137,948
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(447)	(313)	(1,342)	(996)
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	(497)	(286)	(1,492)	(949)
Tax Benefit (Expense)	196	113	589	375
Net Income	(301)	(173)	(903)	(574)
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	(241)	(233)	(725)	(698)
Tax Benefit (Expense)	95	93	286	276
Net Income	(146)	(140)	(439)	(422)
Prior Service Credit | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	81	81	242	242
Net Actuarial Losses | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	$ (322)	$ (314)	$ (967)	$ (940)