Debt (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Long-term Debt
Carrying value long-term debt	$ 642,000	$ 600,000
Less: current maturities	0	(133,000)
Total long-term debt due after one year	642,000	467,000
Term Loan Credit Agreement [Member]
Long-term Debt
Carrying value long-term debt	175,000	0
6.375%, due September 2013 [Member] | Senior Notes [Member]
Long-term Debt
Carrying value long-term debt	0	108,000
Debt Instrument, Interest Rate, Stated Percentage	6.375%
5.75%, due September 2016 [Member] | Senior Notes [Member]
Long-term Debt
Carrying value long-term debt	175,000	175,000
Debt Instrument, Interest Rate, Stated Percentage	5.75%
6.21%, due September 2036 [Member] | Senior Notes [Member]
Long-term Debt
Carrying value long-term debt	100,000	100,000
Debt Instrument, Interest Rate, Stated Percentage	6.21%
5.53%, due September 2012 [Member] | Medium-term Notes [Member]
Long-term Debt
Debt Instrument, Interest Rate, Stated Percentage	5.53%
5.37%, due August 2013 [Member] | Medium-term Notes [Member]
Long-term Debt
Carrying value long-term debt	0	25,000
Debt Instrument, Interest Rate, Stated Percentage	5.37%
5.16%, due May 2015 [Member] | Medium-term Notes [Member]
Long-term Debt
Carrying value long-term debt	20,000	20,000
Debt Instrument, Interest Rate, Stated Percentage	5.16%
7.37%, due October 2015 [Member] | Medium-term Notes [Member]
Long-term Debt
Carrying value long-term debt	22,000	22,000
Debt Instrument, Interest Rate, Stated Percentage	7.37%
5.64%, due December 2015 [Member] | Medium-term Notes [Member]
Long-term Debt
Carrying value long-term debt	50,000	50,000
Debt Instrument, Interest Rate, Stated Percentage	5.64%
6.17%, due June 2017 [Member] | Medium-term Notes [Member]
Long-term Debt
Carrying value long-term debt	20,000	20,000
Debt Instrument, Interest Rate, Stated Percentage	6.17%
7.25%, due November 2017 [Member] | Medium-term Notes [Member]
Long-term Debt
Carrying value long-term debt	20,000	20,000
Debt Instrument, Interest Rate, Stated Percentage	7.25%
5.67%, due January 2018 [Member] | Medium-term Notes [Member]
Long-term Debt
Carrying value long-term debt	20,000	20,000
Debt Instrument, Interest Rate, Stated Percentage	5.67%
6.50%, due August 2033 [Member] | Medium-term Notes [Member]
Long-term Debt
Carrying value long-term debt	20,000	20,000
Debt Instrument, Interest Rate, Stated Percentage	6.50%
6.13%, due October 2034 [Member] | Medium-term Notes [Member]
Long-term Debt
Carrying value long-term debt	$ 20,000	$ 20,000
Debt Instrument, Interest Rate, Stated Percentage	6.13%