Income Taxes - Summary of Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of the year	$ 1,198	$ 4,210	$ 3,860
Additions related to tax positions taken in prior years	74	155	350
Reductions due to resolution of uncertain tax position		(3,167)	0
Balance at the end of the year	$ 1,272	$ 1,198	$ 4,210