Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net Income	$ 45,881	$ 43,493	$ 141,719	$ 137,948
Other Comprehensive Income (Loss), Net of Tax:
Net Unrealized Gains (Losses) on Investment Securities	444	(5,528)	8,444	8,323
Defined Benefit Plans	146	140	439	422
Total Other Comprehensive Income (Loss)	590	(5,388)	8,883	8,745
Comprehensive Income	$ 46,471	$ 38,105	$ 150,602	$ 146,693