Long-term Debt (Schedule of Long-term Debt) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Mar. 31, 2014	Sep. 30, 2013
Total debt	$ 605,000	$ 550,000
Current portion of long-term debt	0	(100,000)
Short-term Debt	21,000	0
Long-term debt, excluding current portion	584,000	450,000
Domestic Line Of Credit [Member]
Interest rate		1.06%
Maturity date	Dec. 20, 2013
Series B Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	0	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
Series J Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	50,000	0
Debt Instrument, Description of Variable Rate Basis	LIBOR
Basis Spread On Variable Rate	1.25%
Maturity date	Nov. 15, 2020
Series G Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	50,000	0
Interest rate	3.42%
Maturity date	Nov. 15, 2020
Series H Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	25,000	0
Interest rate	4.03%
Maturity date	Nov. 15, 2023
Series I Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	25,000	0
Interest rate	4.18%
Maturity date	Nov. 15, 2025
Series K Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	50,000	0
Interest rate	4.03%
Maturity date	Nov. 15, 2023
Series L Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	50,000	0
Interest rate	4.18%
Maturity date	Nov. 15, 2025
Domestic Line Of Credit [Member]
Long-term debt balance	0	200,000
Debt Instrument, Description of Variable Rate Basis	prime rate or an adjusted LIBOR
Revolving Credit Facility [Member]
Credit facility effective interest rate on outstanding borrowing	1.20%
Long-term debt, excluding current portion	84,000
Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument, Description of Variable Rate Basis	0.85%
Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument, Description of Variable Rate Basis	1.65%
Revolving Credit Agreement [Member]
Long-term debt balance	105,000	0
Debt Instrument, Description of Variable Rate Basis	LIBOR
Short-term Debt	$ 21,000
Chinese Credit Facility, RMB Denominated Loan [Member]
Debt Instrument, Description of Variable Rate Basis	interest at the prevailing interest rate offered by the People's Bank of China on the date of borrowing, plus a margin equal to 25% of that prevailing rate
Chinese Credit Facility, USD Denominated Loan [Member]
Debt Instrument, Description of Variable Rate Basis	interest at the lender's cost of borrowing rate at the date of borrowing, plus 3%