Cash and Equivalents - Components of Cash and Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 61,523	$ 59,763	$ 54,711
Other assets	1,000	1,000
Institutional Money Market Funds [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	20,540	20,421
Other Restricted Cash [Member]
Cash and Cash Equivalents [Line Items]
Other assets	1,000	1,000
Cash [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 40,983	$ 39,342