Debt (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument
$870 million Credit Agreement, interest at LIBOR plus 105 basis points	$ 197,131,000	$ 376,715,000
Other Local Arrangements	41,600,000	28,300,000
Total Debt, Long-term and Short-term	388,731,000	505,015,000
Less: current portion	(41,600,000)	(28,300,000)
Long-term debt	347,131,000	476,715,000
Senior Notes, Face Amount	50,000,000
6.3% Senior Notes
Debt Instrument
$100 million Senior Notes, interest at 6.30%, due June 25, 2015	100,000,000	100,000,000
Senior Notes, Face Amount	100,000,000
Senior Notes, Stated Interest Rate	6.30%
Maturity Date	Jun. 25, 2015
3.67% Percent Notes
Debt Instrument
$100 million Senior Notes, interest at 6.30%, due June 25, 2015	50,000,000	0
Senior Notes, Face Amount	50,000,000
Senior Notes, Stated Interest Rate	3.67%
Maturity Date	Dec. 17, 2022
$880 million Credit Agreement, Basis Spread on Variable Rate	0.85%
$870 Credit Agreement
Debt Instrument
Maturity Date	Dec. 20, 2016
Credit Agreement Borrowing Capacity	$ 880,000,000