Fair Value Measurements - Carrying Values and Estimated Fair Values of Other Financial Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Sep. 30, 2012
Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying values and estimated fair values of other financial assets and liabilities	$ 1,276,122	$ 1,262,072
Carrying Amount | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	1,223,485	1,201,067
Mandatory Convertible Subordinated Notes	0	9,402
Carrying Amount | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior Subordinated Notes	52,637	51,603
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying values and estimated fair values of other financial assets and liabilities	1,358,542	1,287,813
Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior Notes	1,305,905	1,228,745
Mandatory Convertible Subordinated Notes	0	7,465
Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Junior Subordinated Notes	$ 52,637	$ 51,603