Significant Accounting Policies Revenue From Contracts with Customers ASU 2014-09 (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Summary Of Significant Accounting Policies [Line Items]
Trade accounts receivable, net	$ 648,525	$ 454,637	$ 528,362
Inventories	833,719	721,290	830,887
Accrued liabilities	90,360	123,602	110,325
Deferred income taxes	274,086	262,394	416,118
Retained earnings	1,897,417	$ 1,809,845	$ 1,589,498
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Trade accounts receivable, net	69,400
Inventories	(56,600)
Accrued liabilities	900
Deferred income taxes	2,800
Retained earnings	$ 9,100