Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 153,804	$ 225,913	$ 219,602
Other Comprehensive Income (Loss), Net of Tax:
Net Unrealized Gains (Losses) on Investment Securities	43,428	22,677	(6,525)
Defined Benefit Plans	(4,494)	(2,746)	(2,326)
Other Comprehensive Income (Loss)	38,934	19,931	(8,851)
Comprehensive Income	$ 192,738	$ 245,844	$ 210,751