Summary of Significant Accounting Policies - Components of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 59,763	$ 57,072	$ 47,226	$ 49,973
Institutional Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	20,421	20,104
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	39,342	36,968
Cash and Equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	1,000	1,000
Cash and Equivalents [Member] | Other Restricted Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 1,000	$ 1,000