Basis of Presentation and Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 549,889	$ 489,413	$ 978,428	$ 907,217
Customer deposits	27,316		27,316		$ 18,937
Contract with customer, liability, revenue recognized	6,900		15,200
Homebuilding revenue
Disaggregation of Revenue [Line Items]
Total revenue	547,417	487,986	971,646	905,385
Land sales and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,472	$ 1,427	$ 6,782	$ 1,832