Organization, Basis of Presentation and Recent Accounting Pronouncements (Recent Accounting Pronouncements) (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating expenses	$ 448,920	$ 374,987	$ 1,254,726	$ 1,082,421
Selling, General and Administrative Expenses	131,081	228,051	497,504	662,313
Income from Operations	60,739	26,950	170,579	86,944
Non-operating pension and postretirement benefit income	(22,214)	(17,621)	(66,641)	(55,042)
Income before income taxes	$ 135,070	38,244	$ 254,370	127,929
Accounting Standards Update 2017-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating expenses		374,987		1,082,421
Selling, General and Administrative Expenses		228,051		662,313
Income from Operations		26,950		86,944
Non-operating pension and postretirement benefit income		17,621		55,042
Income before income taxes		38,244		127,929
Accounting Standards Update 2017-07 [Member] | Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating expenses		352,635		1,011,553
Selling, General and Administrative Expenses		232,782		678,139
Income from Operations		44,571		141,986
Non-operating pension and postretirement benefit income		0		0
Income before income taxes		38,244		127,929
Accounting Standards Update 2017-07 [Member] | Restatement Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating expenses		22,352		70,868
Selling, General and Administrative Expenses		(4,731)		(15,826)
Income from Operations		(17,621)		(55,042)
Non-operating pension and postretirement benefit income		17,621		55,042
Income before income taxes		$ 0		$ 0