Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Sep. 30, 2012
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	$ 96.7		$ 298.0
Homebuilding [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	96.7
Other Investments	18.6		0
Homebuilding [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Other Investments	0	[1]
Homebuilding [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Other Investments	0	[1]
Homebuilding [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Other Investments	18.6	[1]	0	[1]
Homebuilding [Member] | Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Other Investments	18.6	[1]
Financial Services [Member]
Fair value balance sheet items measured on a recurring basis
Mortgage loans held for sale	307.9		345.3
Financial Services [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Mortgage loans held for sale	0		0
Financial Services [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Interest rate lock commitments [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	0		0
Financial Services [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Forward sales of MBS [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	0		0
Financial Services [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Best-efforts and mandatory commitments [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	0		0
Financial Services [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Mortgage loans held for sale	300.2	[2]	345.3	[2]
Financial Services [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Interest rate lock commitments [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	2.3	[3]	6.1	[3]
Financial Services [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Forward sales of MBS [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	(0.5)	[3]	(6.9)	[3]
Financial Services [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Best-efforts and mandatory commitments [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	(0.2)	[3]	(0.8)	[3]
Financial Services [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Mortgage loans held for sale	7.7	[2]	0	[2]
Financial Services [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Interest rate lock commitments [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	0	[3]	0	[3]
Financial Services [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Forward sales of MBS [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	0	[3]	0	[3]
Financial Services [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Best-efforts and mandatory commitments [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	0	[3]	0	[3]
Financial Services [Member] | Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Mortgage loans held for sale	307.9	[2]	345.3	[2]
Financial Services [Member] | Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Interest rate lock commitments [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	2.3	[3]	6.1	[3]
Financial Services [Member] | Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Forward sales of MBS [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	(0.5)	[3]	(6.9)	[3]
Financial Services [Member] | Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Best-efforts and mandatory commitments [Member]
Fair value balance sheet items measured on a recurring basis
Fair value of interest rate derivatives	(0.2)	[3]	(0.8)	[3]
US Treasury Securities [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	12.1		75.7
US Treasury Securities [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	12.1		75.7
US Treasury Securities [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	0		0
US Treasury Securities [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	0		0
US Treasury Securities [Member] | Homebuilding [Member] | Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	12.1		75.7
Government Agency and Corporate Debt Securities [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	0		0
Government Agency and Corporate Debt Securities [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	79.6		212.3
Government Agency and Corporate Debt Securities [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	0		0
Government Agency and Corporate Debt Securities [Member] | Homebuilding [Member] | Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	79.6		212.3
Certificates of Deposit [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	5.0		10.0
Certificates of Deposit [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	0		0
Certificates of Deposit [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	5.0		10.0
Certificates of Deposit [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	0		0
Certificates of Deposit [Member] | Homebuilding [Member] | Estimated Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair value balance sheet items measured on a recurring basis
Marketable securities, available-for-sale	$ 5.0		$ 10.0

[1] In October 2012, the Company purchased $18.6 million of defaulted debt securities which are secured by residential real estate. The Company intends to foreclose and take possession of the residential real estate in order to develop the property and ultimately build and sell homes. These securities are classified as available for sale and are included in other assets in the Company's consolidated balance sheets. At December 31, 2012, the Company valued these securities at the recent October 2012 transaction price, which is considered to be the best initial estimate of fair value.

[2] Mortgage loans held for sale are reflected at fair value. Interest income earned on mortgage loans held for sale is based on contractual interest rates and included in financial services interest and other income. Mortgage loans held for sale includes $7.7 million of loans originated under the fair value option which the Company has not sold into the secondary market, but plans to sell as market conditions permit. The fair value of these mortgage loans held for sale is generally calculated considering the secondary market and adjusted for the value of the underlying collateral, including interest rate risk, liquidity risk and prepayment risk; therefore, they were transferred from a Level 2 valuation to a Level 3 valuation during the three months ended December 31, 2012.

[3] Fair value measurements of these derivatives represent changes in fair value since inception. These changes are reflected in the balance sheet and included in financial services revenues on the consolidated statement of operations.