Long-Term Debt Schedule of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Total long-term debt	$ 1,837,372	$ 2,369,262
Current portion of long-term debt	422,012	247,544
Long-term debt	1,415,360	2,121,718
Senior Notes | 1.875% Senior Notes
Debt Instrument [Line Items]
Total long-term debt	463,575	719,617
Senior Notes | 3.00% Senior Notes
Debt Instrument [Line Items]
Total long-term debt	0	248,714
Senior Notes | 4.15% Senior Notes
Debt Instrument [Line Items]
Total long-term debt	421,628	421,141
Senior Notes | 4.50% Senior Notes
Debt Instrument [Line Items]
Total long-term debt	174,325	347,620
Senior Notes | 5.45% Senior Notes
Debt Instrument [Line Items]
Total long-term debt	345,841	345,687
Commercial Paper
Debt Instrument [Line Items]
Total long-term debt	421,321	247,503
Variable-rate foreign bank loans
Debt Instrument [Line Items]
Total long-term debt	5,298	38,939
Other long-term debt
Debt Instrument [Line Items]
Total long-term debt	$ 5,384	$ 41