Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total long-term Debt	$ 1,476,068	$ 1,837,372
Current portion of long-term debt	39,216	422,012
Long-term debt	1,436,852	1,415,360
Senior Notes | 1.875% Senior Notes
Debt Instrument [Line Items]
Total long-term Debt	482,567	463,575
Senior Notes | 4.15% Senior Notes
Debt Instrument [Line Items]
Total long-term Debt	421,750	421,628
Senior Notes | 4.50% Senior Notes
Debt Instrument [Line Items]
Total long-term Debt	174,401	174,325
Senior Notes | 5.45% Senior Notes
Debt Instrument [Line Items]
Total long-term Debt	345,880	345,841
Commercial paper notes
Debt Instrument [Line Items]
Total long-term Debt	38,500	421,321
Variable-rate foreign bank loans
Debt Instrument [Line Items]
Total long-term Debt	7,560	5,298
Other long-term debt
Debt Instrument [Line Items]
Total long-term Debt	$ 5,410	$ 5,384