Long Term Debt (Narrative) (Details) (USD $)		3 Months Ended		3 Months Ended
	Mar. 31, 2014	Mar. 31, 2014 U.S. Revolver	Mar. 31, 2014 U.S. Revolver Maximum	Mar. 31, 2014 U.S. Revolver Federal Funds Rate	Mar. 31, 2014 U.S. Revolver Eurocurrency Rate	Mar. 31, 2014 Canadian Revolver	Mar. 31, 2014 Canadian Revolver Maximum	Mar. 31, 2014 Canadian Revolver Minimum	Mar. 31, 2014 Industrial Development Revenue Bonds	Oct. 31, 2001 Industrial Development Revenue Bonds
Line Of Credit Facility [Line Items]
Revolving credit facility		$ 75,000,000
Revolving credit interest rate		The interest rate for amounts outstanding under the Amended Credit Agreement for the U.S. Revolver is a floating rate based upon the higher of the Federal Funds Rate plus 0.5%, the bank’s prime rate, or the Eurocurrency rate plus 1.00%.
Basis spread on variable rate				0.50%	1.00%
Margin			1.75%				1.75%	0.50%
Outstanding letters of credit		21,900,000				100,000
Amount of credit facility remaining borrowing capacity		53,100,000				8,900,000
Credit facility expiration date		Dec. 31, 2018				Feb. 28, 2015
Percentage of voting capital stock pledged as collateral		100.00%
Non-domestic subsidiaries of voting capital stock		66.00%
Revolving credit facility, current borrowing capacity						9,000,000
Borrowings										8,000,000
Reimbursement agreement requires annual redemptions									400,000
Balance in the restricted sinking fund	$ 200,000
Interest rate									0.25%