Debt (Details Textual) (USD $)	12 Months Ended				12 Months Ended		12 Months Ended
	Dec. 31, 2012 Institutions	Dec. 31, 2011	Dec. 31, 2012 Commercial paper [Member]	Dec. 31, 2011 Commercial paper [Member]	Dec. 31, 2012 Medium-term Notes [Member]	Feb. 28, 2012 350 million unsecured medium-term notes due 2017 [Member]	Dec. 31, 2012 350 million unsecured medium-term notes due 2018 [Member]	Aug. 31, 2012 350 million unsecured medium-term notes due 2018 [Member]	Jun. 30, 2011 Letter of Credit [Member]	Jun. 30, 2011 Global Revolving Credit Facility [Member]
Debt (Textual) [Abstract]
Unamortized original issue discounts	$ 8,765,000	$ 9,351,000
Aggregate notional amount of interest rate swaps	550,000,000	550,000,000
Maximum borrowing capacity under global revolving credit facility									75,000,000	900,000,000
Number of lending institutions	12
Letter of credit outstanding amount	0
Annual facility fees minimum	0.10%
Annual facility fees maximum	0.325%
Current annual facility fee	0.15%
Total facility size		900,000,000
Global revolving credit facility covenant terms, debt to consolidated tangible net worth ratio	less than or equal to 300%
Debt to consolidated tangible net worth ratio	180.00%
Amount available under the global revolving credit facility	538,000,000
Commercial paper classified as long term debt			353,090,000	415,936,000
Face amount of unsecured medium-term notes issued						350,000,000		350,000,000
Repurchase price condition of notes					101% of Principal Plus Accrued And Unpaid Interest		101%
Total available proceeds under trade receivables purchase and sale program	175,000,000
Number of days under trade trade receivables purchase and sale program	364 days
Amount outstanding under trade receivables purchase and sale program	$ 0	$ 0