Debt and Credit Agreements (Details)	12 Months Ended												1 Months Ended	12 Months Ended
	Dec. 31, 2012 USD ($)		Dec. 31, 2011 USD ($)	Dec. 31, 2011 Commercial paper Short-term debt USD ($)	Dec. 31, 2012 U.S. commercial paper program USD ($)	Dec. 31, 2011 U.S. commercial paper program USD ($)	Dec. 31, 2012 U.S. commercial paper program Long-term debt USD ($)	Dec. 31, 2012 Euro commercial paper program USD ($)	Dec. 31, 2012 Euro commercial paper program EUR (€)	Dec. 31, 2012 Multi-year revolving credit facility USD ($)		Dec. 31, 2012 Bilateral credit facility USD ($)	Mar. 31, 2012 Credit Agreement USD ($) bank	Dec. 31, 2012 Multi-year revolving credit facility USD ($)
Line of Credit Facility [Line Items]
Facility Limit	$ 1,338,900,000				$ 550,000,000			$ 263,900,000	€ 200,000,000	$ 525,000,000	[1]	$ 25,000,000	$ 525,000,000
Outstanding Balance	89,497,000			40,000,000	39,497,000	40,000,000	39,500,000	0		50,000,000	[1]
Available Credit	1,249,403,000	[2]			510,503,000			263,900,000		475,000,000	[1]
Maximum internal borrowing limit	525,000,000
Number of lenders providing credit facility (in banks)													14
Contingent increase to maximum borrowing capacity													550,000,000
Variable basis of interest rates													LIBOR
Write off of previously deferred financing costs														500,000
Short-term borrowings	$ 8,560,000		$ 51,414,000
Weighted average interest rate	4.90%		1.30%

[1] U.S.-based program.

[2] Although the Company has significant available credit, in practice, the Company limits aggregate commercial paper and credit facility borrowings at any one-time to a maximum of $525 million (the amount of the back-up facility).