Debt (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	$ 439,872,000
Less: current portion	(17,959,000)	(41,600,000)
Long-Term Debt
Long-term debt	421,913,000	347,131,000
Debt Instrument, Face Amount	50,000,000
US Dollar Amounts [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	391,526,000
Less: current portion	0
Long-Term Debt
Long-term debt	391,526,000
Other Principal Trading Currencies [Member]
Long-Term Debt, by Current and Noncurrent, and Short-Term Debt
Total debt	48,346,000
Less: current portion	(17,959,000)
Long-Term Debt
Long-term debt	30,387,000
Senior Notes 6 Point 30 Percentage Member
Debt Instrument [Line Items]
Senior Notes	100,000,000
Long-Term Debt
Debt Instrument, Face Amount	100,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.30%
Senior Notes 6 Point 30 Percentage Member | US Dollar Amounts [Member]
Debt Instrument [Line Items]
Senior Notes	100,000,000
Senior Notes 6 Point 30 Percentage Member | Other Principal Trading Currencies [Member]
Debt Instrument [Line Items]
Senior Notes	0
3.67 Percent Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes	50,000,000
Long-Term Debt
Debt Instrument, Interest Rate, Stated Percentage	3.67%
3.67 Percent Senior Notes [Member] | US Dollar Amounts [Member]
Debt Instrument [Line Items]
Senior Notes	50,000,000
3.67 Percent Senior Notes [Member] | Other Principal Trading Currencies [Member]
Debt Instrument [Line Items]
Senior Notes	0
$880 Credit Agreement [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	271,913,000
Long-Term Debt
Line of Credit Facility, Remaining Borrowing Capacity	603,100,000
$880 Credit Agreement [Member] | US Dollar Amounts [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	241,526,000
$880 Credit Agreement [Member] | Other Principal Trading Currencies [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Amount Outstanding	30,387,000
Other Local Arrangements [Member]
Debt Instrument [Line Items]
Other Borrowings	17,959,000
Other Local Arrangements [Member] | US Dollar Amounts [Member]
Debt Instrument [Line Items]
Other Borrowings	0
Other Local Arrangements [Member] | Other Principal Trading Currencies [Member]
Debt Instrument [Line Items]
Other Borrowings	$ 17,959,000