Basis of Presentation and Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Total revenue	$ 489,413	$ 421,260	$ 907,217	$ 823,300
Customer deposits	17,149		17,149		$ 11,539
Contract with customer, liability, revenue recognized	3,900		10,000
Homebuilding revenue
Disaggregation of Revenue [Line Items]
Total revenue	487,986	420,945	905,385	821,927
Land sales and other revenue
Disaggregation of Revenue [Line Items]
Total revenue	$ 1,427	$ 315	$ 1,832	$ 1,373