Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net Income	$ 54,718	$ 44,662	$ 108,758	$ 95,838
Other Comprehensive Income (Loss), Net of Tax:
Net Unrealized Gains (Losses) on Investment Securities	(2,974)	3,106	(12,095)	8,000
Defined Benefit Plans	216	147	432	293
Total Other Comprehensive Income (Loss)	(2,758)	3,253	(11,663)	8,293
Comprehensive Income	$ 51,960	$ 47,915	$ 97,095	$ 104,131