Debt (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	$ 466,670
Less: current portion	(121,306)	(17,067)
Long-Term Debt
Long-term debt	345,364	395,960
US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	403,166
Less: current portion	(101,355)
Long-Term Debt
Long-term debt	301,811
Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	63,504
Less: current portion	(19,951)
Long-Term Debt
Long-term debt	43,553
6.30% Senior Notes [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	100,000
6.30% Senior Notes [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	100,000
6.30% Senior Notes [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	0
3.67% Senior Notes [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	50,000
3.67% Senior Notes [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	50,000
3.67% Senior Notes [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	0
4.10% Senior Notes [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	50,000
4.10% Senior Notes [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	50,000
4.10% Senior Notes [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	0
Credit facility [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	245,364
Credit facility [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	201,811
Credit facility [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	43,553
Other local arrangements [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	21,306
Other local arrangements [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	1,355
Other local arrangements [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	$ 19,951