Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 59,949	$ 34,742
Other Comprehensive Income (Loss), Net of Tax:
Net Unrealized Gains (Losses) on Investment Securities	(50,050)	41,559
Defined Benefit Plans	441	374
Total Other Comprehensive Income (Loss)	(49,609)	41,933
Comprehensive Income	$ 10,340	$ 76,675