Contingencies - Warranty (Details) $ in Thousands	3 Months Ended		6 Months Ended		42 Months Ended
	Mar. 31, 2018 USD ($) home	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) home	Mar. 31, 2017 USD ($)	Mar. 31, 2018 USD ($) home
Loss Contingencies [Line Items]
Standard product warranty length, minimum			1 year
Standard product warranty length, maximum			2 years
Limited product warranty length (up to)			10 years
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at beginning of period	$ 15,816	$ 32,309	$ 18,091	$ 39,131
Accruals for warranties issued	3,400	3,249	7,613	5,907
Changes in liability related to warranties existing in prior periods	(1,097)	2,463	(3,394)	7,855
Payments made	(3,536)	(12,635)	(7,727)	(27,507)
Balance at end of period	14,583	25,386	14,583	25,386	$ 14,583
Insurance recoveries	200	$ 2,300	400	$ 6,200	82,600
Specific Warranty Issue
Movement in Standard Product Warranty Accrual [Roll Forward]
Product warranty expense					85,000
Specific Warranty Issue | Florida
Movement in Standard Product Warranty Accrual [Roll Forward]
Balance at end of period	2,400		2,400		$ 2,400
Decrease in warranty reserves	$ 200		$ 600
Homes likely to require more than minor repairs | home	709		709		709
Homes have been repaired | home	675		675		675
Product warranty accrual, payments	$ 600		$ 1,700
Estimated remaining warranty costs	$ 2,400		$ 2,400		$ 2,400