Basis of Presentation and Summary of Significant Accounting Policies Basis of Presentation and Summary of Significant Accounting Policies - Business Acquisitions (Details) $ in Thousands		12 Months Ended
	Jul. 13, 2018 USD ($) home lot Community	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Business Acquisition [Line Items]
Document Fiscal Year Focus		2018
Number of single-family communities | Community	27
Goodwill and intangible assets, net		$ 9,751	$ 0
Venture Homes
Business Acquisition [Line Items]
Purchase price, net of cash acquired	$ 60,600
Purchase price paid as of period end, net of cash acquired		57,300
Expected payment on business acquisition in next fiscal quarter		$ 3,300
Number of homes in backlog | home	48
Number of model homes in backlog | home	6
Inventory acquired	$ 56,000
Goodwill and intangible assets, net	9,800
Other assets acquired	600
Accounts payable assumed	5,500
Other liabilities assumed	$ 200
Minimum | Venture Homes
Business Acquisition [Line Items]
Number of lots owned or controlled | lot	1,100