Employee Benefits (Other Comprehensive Income - Retirement Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	$ (12,634)	$ 20,053	$ (5,429)
Prior service benefit	0	(32,697)	(824)
Amortization of:
Net loss	(6,776)	(4,965)	(8,622)
Prior service benefit	9,657	7,407	6,574
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	(4,265)	8,644	4,266
Amortization of:
Net loss	(7,572)	(6,554)	(9,710)
Prior service benefit	3,467	3,467	3,467
Total recognized in other comprehensive income	(8,370)	5,557	(1,977)
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	2,217	1,266	(811)
Amortization of:
Net loss	(882)	(785)	(937)
Prior service benefit	39	39	39
Total recognized in other comprehensive income	$ 1,374	$ 520	$ (1,709)