Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net Income	$ 67,081	$ 57,910	$ 50,539
Other Comprehensive Income (Loss), Before Tax:
Net change in unrealized (losses) gains on securities available-for-sale	(663)	11,825	(16,928)
Net available-for-sale securities losses (gains) reclassified into earnings	34	(41)	(5)
Adjustment to funded status of employee benefit plans	(3,551)	(13,394)	18,299
Other Comprehensive Income (Loss), Before Tax	(4,180)	(1,610)	1,366
Income tax benefit (expense) related to items of other comprehensive income	1,556	471	(478)
Other Comprehensive Income (Loss), After Tax	(2,624)	(1,139)	888
Comprehensive Income	$ 64,457	$ 56,771	$ 51,427