Significant Accounting Policies Net Periodic Pension Cost and Net Postretirement Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Summary Of Significant Accounting Policies [Line Items]
Cost of goods sold	$ 1,102,892	$ 1,061,289	$ 2,840,991	$ 2,611,836
Selling, general and administrative expenses	73,690	75,149	228,691	232,461
Other pension and postretirement income	$ (8,326)	(8,635)	$ (27,536)	(25,192)
Accounting Standards Update 2017-07 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cost of goods sold		6,900		20,000
Selling, general and administrative expenses		1,700		5,200
Other pension and postretirement income		$ (8,600)		$ (25,200)