Summary of Significant Accounting Policies - Summary of Cash, Cash Equivalents and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2016	[1]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 46,735	$ 80,757		$ 31,227
Restricted cash, non-current	579	579		202
Restricted cash, current (within prepaid expenses and other current assets)	84	201		144
Total cash, cash equivalents and restricted cash	$ 47,398	$ 81,537	[1]	$ 31,573	[1]	$ 29,062

[1] Adjusted to reflect the retrospective adoption of Accounting Standards Update (ASU) 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash.