Long-term Debt (Schedule of Long-term Debt) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Long-term debt balance	$ 500,000
Short-term Debt	2,430	$ 0
Long-term debt, excluding current portion	850,000	710,000
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]
Variable interest rate	1.58%
Series J Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	$ 50,000	$ 50,000
Basis Spread On Variable Rate	1.25%	1.25%
Maturity date	Nov. 15, 2020	Nov. 15, 2020
Series G Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	$ 50,000	$ 50,000
Interest rate	3.42%	3.42%
Maturity date	Nov. 15, 2020	Nov. 15, 2020
Series H Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	$ 25,000	$ 25,000
Interest rate	4.03%	4.03%
Maturity date	Nov. 15, 2023	Nov. 15, 2023
Series I Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	$ 25,000	$ 25,000
Interest rate	4.18%	4.18%
Maturity date	Nov. 15, 2025	Nov. 15, 2025
Series K Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	$ 50,000	$ 50,000
Interest rate	4.03%	4.03%
Maturity date	Nov. 15, 2023	Nov. 15, 2023
Series L Notes [Member] | Notes Payable to Banks [Member]
Long-term debt balance	$ 50,000	$ 50,000
Interest rate	4.18%	4.18%
Maturity date	Nov. 15, 2025	Nov. 15, 2025
Revolving Credit Facility [Member]
Long-term debt balance	$ 350,000	$ 210,000
Revolving Credit Facility [Member] | Minimum [Member]
Basis Spread On Variable Rate	0.85%
Revolving Credit Agreement [Member]
Credit facility effective interest rate on outstanding borrowing		1.21%
Amended Revolving Credit Agreement [Member]
Credit facility effective interest rate on outstanding borrowing	1.44%
Maturity date	Apr. 01, 2020
Amended Revolving Credit Agreement [Member] | Minimum [Member]
Basis Spread On Variable Rate	0.85%
Amended Revolving Credit Agreement [Member] | Maximum [Member]
Basis Spread On Variable Rate	1.65%
Chinese Credit Facility, RMB Denominated Loan [Member]
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 15% of that prevailing rate
Chinese Credit Facility, USD Denominated Loan [Member]
Variable Rate Basis	interest at the lender's cost of borrowing rate at the date of borrowing, plus 3%