Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net Income	$ 181,461	$ 160,704	$ 163,042
Other Comprehensive Income (Loss), Net of Tax:
Net Unrealized Gains (Losses) on Investment Securities	(10,318)	(2,125)	16,858
Defined Benefit Plans, Net	(31)	5,254	(11,721)
Other Comprehensive Income (Loss)	(10,349)	3,129	5,137
Comprehensive Income	$ 171,112	$ 163,833	$ 168,179