Accumulated Other Comprehensive Income (Loss) - AOCI Reclass to IS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for Income Tax	$ (19,025)	$ (7,461)
Net Income	59,949	34,742
Salaries and Benefits	(56,251)	(54,463)
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(534)	(366)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Unrealized Gains(Losses) of Investment Securities Transferred from AFS to HTM
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Income	(125)	(65)
Provision for Income Tax	32	17
Net Income	(93)	(48)
Reclassification out of Accumulated Other Comprehensive Income | Sale of Investment Securities Available-for-Sale
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for Income Tax	0	(21)
Net Income	0	56
Sale of Investment Securities Available-for-Sale	0	77
Reclassification out of Accumulated Other Comprehensive Income | Prior Service Credit
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	61	61
Reclassification out of Accumulated Other Comprehensive Income | Net Actuarial Losses
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	(662)	(570)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Defined Benefit Plan Items
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for Income Tax	160	135
Net Income	(441)	(374)
Salaries and Benefits	$ (601)	$ (509)