Long Term Debt (Narrative) (Details) - USD ($)	3 Months Ended
	Dec. 31, 2016	Oct. 31, 2001
U.S. Revolver
Line Of Credit Facility [Line Items]
Percentage of voting capital stock pledged as collateral	100.00%
Non-domestic subsidiaries of voting capital stock	65.00%
Revolving credit facility	$ 75,000,000.0
Revolving credit interest rate	The interest rate for amounts outstanding under 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%.
Outstanding letters of credit	$ 20,300,000
Credit facility expiration date	Dec. 31, 2018
Amount of credit facility remaining borrowing capacity	$ 54,700,000
Revolving credit facility borrowings, outstanding amount	$ 0
U.S. Revolver | Maximum
Line Of Credit Facility [Line Items]
Basis spread on variable rate	1.75%
U.S. Revolver | Federal Funds Rate
Line Of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
U.S. Revolver | Eurocurrency Rate
Line Of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Canadian Revolver
Line Of Credit Facility [Line Items]
Revolving credit facility	$ 7,437,000
Outstanding letters of credit	$ 0
Credit facility expiration date	Mar. 31, 2018
Amount of credit facility remaining borrowing capacity	$ 7,400,000
Revolving credit facility borrowings, outstanding amount	$ 0
Canadian Revolver | Maximum
Line Of Credit Facility [Line Items]
Basis spread on variable rate	1.75%
Canadian Revolver | Minimum
Line Of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Industrial Development Revenue Bonds
Line Of Credit Facility [Line Items]
Borrowings		$ 8,000,000.0
Reimbursement agreement requires annual redemptions	$ 400,000
Interest rate	0.90%