Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Mar. 31, 2018	Sep. 30, 2017
Assets:
Marketable securities			$ 13,791
Cash deposits		$ 96,600	90,300
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	[1]	11,237	15,295
Marketable securities	[2]	16,134	13,791
Total		27,371	29,086
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1)
Assets:
Cash equivalents	[1]	11,237	15,295
Marketable securities	[2]	16,134	13,791
Total		$ 27,371	$ 29,086

[1] Included in cash and cash equivalents on our condensed consolidated balance sheet at March 31, 2018 and September 30, 2017. Not included in these tables are cash deposits of $96.6 million and $90.3 million at March 31, 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 March 31, 2018 and September 30, 2017.