Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Jun. 30, 2018	Sep. 30, 2017
Assets:
Marketable securities			$ 13,791
Cash deposits		$ 87,400	90,300
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	[1]	32,500	15,295
Marketable securities	[2]	16,930	13,791
Total		49,430	29,086
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1)
Assets:
Cash equivalents	[1]	32,500	15,295
Marketable securities	[2]	16,930	13,791
Total		$ 49,430	$ 29,086

[1] Included in cash and cash equivalents on our condensed consolidated balance sheet at June 30, 2018 and September 30, 2017. Not included in these tables are cash deposits of $87.4 million and $90.3 million at June 30, 2018 and September 30, 2017, respectively.

[2] Represents securities held under a supplemental retirement and savings plan for senior management employees, which are distributed upon termination or retirement of the employees. Included in marketable securities on our condensed consolidated balance sheet at June 30, 2018 and September 30, 2017.