Debt (Details) (USD $)				3 Months Ended		3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Dec. 31, 2011 Credit Agreement	Mar. 31, 2012 Credit Agreement Minimum	Feb. 29, 2008 Credit Agreement Minimum	Mar. 31, 2012 Credit Agreement Maximum	Feb. 29, 2008 Credit Agreement Maximum	Feb. 29, 2008 Credit Agreement Prime or Federal Funds	Feb. 29, 2008 Credit Agreement LIBOR Minimum	Feb. 29, 2008 Credit Agreement LIBOR Maximum	Mar. 31, 2012 Credit Agreement Federal Funds	Mar. 31, 2012 U.S. Dollar term loan under the Amended Credit Agreement	Dec. 31, 2011 U.S. Dollar term loan under the Amended Credit Agreement	Feb. 29, 2008 U.S. Dollar term loan under the Amended Credit Agreement	Mar. 31, 2012 U.S. Dollar revolving loans under the Amended Credit Agreement	Dec. 31, 2011 U.S. Dollar revolving loans under the Amended Credit Agreement	Feb. 29, 2008 U.S. Dollar revolving loans under the Amended Credit Agreement	Mar. 31, 2012 U.S. Dollar revolving loans under the Amended Credit Agreement Minimum	Mar. 31, 2012 U.S. Dollar revolving loans under the Amended Credit Agreement Maximum	Mar. 31, 2012 U.S. Dollar revolving loans under the Amended Credit Agreement Adjusted LIBOR	Mar. 31, 2012 U.S. Dollar revolving loans under the Amended Credit Agreement Adjusted LIBOR Minimum	Mar. 31, 2012 U.S. Dollar revolving loans under the Amended Credit Agreement Adjusted LIBOR Maximum	Mar. 31, 2012 US Dollar note under the Note Purchase Agreement	Mar. 31, 2012 Capital lease obligations	Dec. 31, 2011 Capital lease obligations	Mar. 31, 2012 Other revolving loans
Debt
Total debt	$ 319,600,000	$ 303,100,000										$ 75,000,000	$ 82,500,000			$ 216,500,000							$ 240,000,000	$ 4,600,000	$ 4,100,000
Current portion of long-term debt	(76,300,000)	(83,700,000)
Total long-term debt, less current portion	243,300,000	219,400,000
Maximum commitment															250,000,000		230,000,000									193,600,000
Term facility														150,000,000
Interest rate added to base rate (as a percent)								0.50%	0.40%	1.25%	0.50%									1.00%	0.80%	1.65%
Facility fee (as a percent)					0.10%		0.20%											0.20%	0.35%
Weighted Average Interest Rate (as a percent)															0.00%											0.00%
leverage ratio						3.0
Interest coverage ratio				3.0
Outstanding Borrowings			$ 216,500,000