Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Income Taxes
Interest (income) expense	$ (73)	$ 204	$ 0
Unrecognized tax benefits	1,829	2,055	0	$ 0
Accrued interest	132
Unrecognized tax benefits if recognized would impact the reported effective tax rate	940
State and Local Jurisdiction
Income Taxes
Decrease in income tax expense due to state tax flow through of accelerated depreciation	$ 2,537	$ 1,344	$ 1,539