Supplemental Cash Flow Information - Supplemental Disclosure of Non-cash Activity (Details) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016
Supplemental disclosure of non-cash activity:
Non-cash land acquisitions	$ 0	$ 5,197
Land acquisitions for debt	0	6,304
Supplemental disclosure of cash activity:
Interest payments	43,433	50,153
Income tax payments	10	91
Tax refunds received	39	3
Reconciliation of cash, cash equivalents, and restricted cash:
Cash and cash equivalents	158,787	138,809	$ 292,147
Restricted cash	12,783	14,696	12,462
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows	$ 171,570	$ 153,505	$ 304,609	$ 243,276