Debt (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	$ 461,658
Less: current portion	(17,931)	(41,600)
Long-Term Debt
Long-term debt	443,727	347,131
US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	420,342
Less: current portion	0
Long-Term Debt
Long-term debt	420,342
Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	41,316
Less: current portion	(17,931)
Long-Term Debt
Long-term debt	23,385
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
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
Credit facility [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	293,727
Credit facility [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	270,342
Credit facility [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	23,385
Other local arrangements [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	17,931
Other local arrangements [Member] | US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	0
Other local arrangements [Member] | Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	$ 17,931