Summary of Significant Accounting Policies - Notes Receivable (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gain on restructured notes receivable	$ (3,000)	$ 0	$ 3,048	$ 0
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restructured notes receivable, estimated settlement amount		$ 14,000