Employee Benefits (Other Comprehensive Income, Other Postretirement Benefit Plans) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	$ 20,053	$ (5,429)	$ 54,328
Prior service benefit	(32,697)	(824)	(34,200)
Amortization of:
Prior service benefit	7,407	6,574	7,659
Net gain	(4,965)	(8,622)	(6,182)
Other Postretirement Benefit Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net (gain) loss	10,143	(8,884)	3,496
Prior service benefit	(32,697)	(824)	0
Amortization of:
Prior service benefit	3,901	3,068	4,753
Net gain	2,374	2,025	2,671
Total recognized in other comprehensive income	$ (16,279)	$ (4,615)	$ 10,920