Summary of Significant Accounting Policies Business Acquisitions (Details) $ in Millions	3 Months Ended			12 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2013 USD ($)	Apr. 30, 2015 Lot Home	May. 31, 2014 USD ($) Lot Home	Oct. 31, 2013 Lot Home
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired				$ 70.9	$ 244.1	$ 9.4
Crown Communities [Member]
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement		May 09, 2014
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory								$ 140.5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment								1.9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets								4.9
Goodwill, Acquired During Period		$ 53.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill								11.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities								$ (3.0)
Payments to Acquire Businesses, Net of Cash Acquired		209.6
Business Acquisition, Number of Homes Acquired | Home								640
Business Acquisition, Number of Finished Lots Acquired | Lot								2,350
Business Acquisition, Number of Lots Under Option Contracts | Lot								3,400
Business Acquisition, Sales Order Backlog Acquired (Homes) | Home								431
RegentHomes [Member]
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement			Oct. 04, 2013
Payments to Acquire Businesses, Net of Cash Acquired			$ 34.5
Business Acquisition, Number of Homes Acquired | Home									240
Business Acquisition, Number of Finished Lots Acquired | Lot									300
Business Acquisition, Number of Lots Under Option Contracts | Lot									600
Business Acquisition, Sales Order Backlog Acquired (Homes) | Home									213
Pacific Ridge Homes [Member]
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement	Apr. 24, 2015
Payments to Acquire Businesses, Net of Cash Acquired	$ 70.9
Business Acquisition, Number of Homes Acquired | Home							90
Business Acquisition, Number of Finished Lots Acquired | Lot							350
Business Acquisition, Number of Lots Under Option Contracts | Lot							400
Business Acquisition, Sales Order Backlog Acquired (Homes) | Home							42
Southeast [Member] | Crown Communities [Member]
Business Acquisition [Line Items]
Goodwill, Acquired During Period		34.1
East [Member] | Crown Communities [Member]
Business Acquisition [Line Items]
Goodwill, Acquired During Period		$ 19.5