Contingencies - Narrative (Details) $ in Thousands	12 Months Ended			51 Months Ended
	Sep. 30, 2018 USD ($) home	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2018 USD ($) home	Sep. 30, 2015 USD ($)
Loss Contingencies [Line Items]
Limited product warranty length	10 years
Accrued warranty expenses	$ 15,331	$ 18,091	$ 39,131	$ 15,331	$ 27,681
Insurance recoveries	200	4,800
Excess insurance recovery			3,600
Accrued amounts for litigation and other contingent liabilities	3,700	3,900		3,700
Specific Warranty Issue
Loss Contingencies [Line Items]
Product warranty expense				$ 85,000
Specific Warranty Issue | Florida
Loss Contingencies [Line Items]
Product warranty expense	$ 600	5,200
Numer of homes likely to require more than minor repairs | home	707			707
Number of homes that have been repaired | home	685			685
Accrued product warranty, decrease for payments	$ 2,400
Accrued warranty expenses	1,700	$ 4,700		$ 1,700
Performance Bonds
Loss Contingencies [Line Items]
Letters of credit secured using cash collateral	38,100			38,100
Cash collateral in restricted accounts securing letters of credit	$ 237,800			$ 237,800
Minimum
Loss Contingencies [Line Items]
Standard product warranty period	1 year
Maximum
Loss Contingencies [Line Items]
Standard product warranty period	2 years
Settled Litigation | Insurance Settlement
Loss Contingencies [Line Items]
Insurance recoveries			$ 15,500