Employee and Retiree Benefit Plans (Effects of Fair Value Measurements Using Significant Unobservable Inputs on Changes in Level 3 Plan Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total beginning balance	$ 563,825
Total ending balance	487,094	$ 563,825
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total beginning balance	37,950
Total ending balance	35,055	37,950
Defined Benefit Plan, Hedged Funds And Other Alternative Strategies [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total beginning balance	37,950	34,114
Relating to assets held at the reporting date	(2,921)	3,836
Relating to assets sold during the period
Purchases, sales and settlements
Total ending balance	$ 35,029	$ 37,950