Cash and Equivalents - Components of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 57,930	$ 57,072	$ 55,253	$ 47,226
Institutional Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	20,318	20,104
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	37,612	36,968
Other Assets [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	1,000	1,000
Other Assets [Member] | Other Restricted Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 1,000	$ 1,000