Employee Benefits (Net Periodic Benefit Cost) (Details) - Other Postretirement Benefit Plan - 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]
Decrease In Service and Interest Component of Net Periodic Benefit Cost		$ 800
Service cost	$ 2,236	2,769	$ 3,454
Interest cost	2,723	3,167	4,035
Expected return on plan assets	(1,907)	(1,835)	(2,070)
Amortization of:
Prior service benefit	(6,151)	(3,901)	(3,068)
Net gain	(1,678)	(2,374)	(2,025)
Net periodic benefit cost (benefit)	$ (4,777)	$ (2,174)	$ 326