Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Sep. 30, 2017
Summary Of Accounting And Financial Policies [Line Items]
Outstanding letter of credit	$ 608	$ 608
ASU 2016-18 [Member]
Summary Of Accounting And Financial Policies [Line Items]
Outstanding letter of credit	$ 608

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant