Shareholders' Equity - AOCI Reclass to IS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for Income Tax	$ 35,320	$ 59,913	$ 50,624
Net Income	153,804	225,913	219,602
Salaries and Benefits	207,329	216,106	213,208
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(1,788)	(1,472)	(2,553)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Unrealized Gains(Losses) of Investment Securities Transferred from AFS to HTM [Member]
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Interest Income	(397)	(833)	(2,164)
Provision for Income Tax	105	221	569
Net Income	(292)	(612)	(1,595)
Reclassification out of Accumulated Other Comprehensive Income | Sales of Investment Securities Available-for-Sale
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for Income Tax	(50)	(49)
Net Income	27	103
Investment Securities Gains (Losses), Net	77	152
Reclassification out of Accumulated Other Comprehensive Income | Prior Service Credit
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	246	288	567
Reclassification out of Accumulated Other Comprehensive Income | Net Actuarial Losses
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Salaries and Benefits	(2,318)	(1,598)	(1,835)
Reclassification out of Accumulated Other Comprehensive Income | Amortization of Defined Benefit Pension Items
Reclassification Out of Accumulated Other Comprehensive Income [Line Items]
Provision for Income Tax	549	347	310
Net Income	(1,523)	(963)	(958)
Salaries and Benefits	$ (2,072)	$ (1,310)	$ (1,268)