Significant Accounting Policies Net Periodic Pension Cost and Net Postretirement Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Summary Of Significant Accounting Policies [Line Items]
Cost of goods sold	$ 885,853	$ 863,120	$ 1,738,101	$ 1,550,547
Selling, general and administrative expenses	78,253	88,654	154,998	157,313
Other pension and postretirement income	$ (9,612)	(8,231)	$ (19,210)	(16,557)
Accounting Standards Update 2017-07 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cost of goods sold		6,500		13,100
Selling, general and administrative expenses		1,700		3,500
Other pension and postretirement income		$ (8,200)		$ (16,600)