Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 37,840	$ 52,052	$ 111,490	$ 167,770
Other Comprehensive Income (Loss), Net of Tax:
Net Unrealized Gains (Losses) on Investment Securities	(4,900)	5,405	44,389	28,533
Defined Benefit Plans	374	245	1,122	736
Total Other Comprehensive Income (Loss)	(4,526)	5,650	45,511	29,269
Comprehensive Income	$ 33,314	$ 57,702	$ 157,001	$ 197,039