Credit Facilities, Short-term Borrowings and Long-term Debt (Schedule of Long-term Debt) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Mar. 31, 2013	Sep. 30, 2012
Long-term debt balance	$ 550,000	$ 391,875
Less: current portion	(100,000)	(7,500)
Long-term debt, less current portion	450,000	384,375
2008 Term Loan [Member] | Medium-term Notes [Member]
Long-term debt balance	0	41,875
Variable interest rate	0.00%	1.47%
Maturity date		Oct. 01, 2013
Series B Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	100,000	100,000
Interest rate	5.63%	5.63%
Maturity date	Oct. 01, 2013	Oct. 01, 2013
Series C Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	50,000	50,000
Interest rate	5.92%	5.92%
Maturity date	Oct. 01, 2015	Oct. 01, 2015
Series D Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	100,000	100,000
Interest rate	6.39%	6.39%
Maturity date	Oct. 01, 2018	Oct. 01, 2018
Series E Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	57,000	57,000
Interest rate	7.81%	7.81%
Maturity date	Apr. 03, 2016	Apr. 03, 2016
Series F Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	43,000	43,000
Interest rate	8.24%	8.24%
Maturity date	Apr. 03, 2019	Apr. 03, 2019
Total Accumulated Other Comprehensive (Loss) Earnings [Member] | Designated as Hedging Instrument [Member]
Fair value hedge adjustment for unrecognized discontinued hedge gains	(521)	(607)
Domestic Line of Credit [Member]
Credit facility effective interest rate on outstanding borrowing	1.12%
Domestic Line of Credit [Member] | Line of Credit [Member]
Long-term debt balance	$ 200,000
Credit facility effective interest rate on outstanding borrowing	1.12%