Fair Value Measurements - Financial Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands		Jun. 30, 2020	Sep. 30, 2019
Assets:
Marketable securities		$ 23,549	$ 20,222
Cash deposits		101,300	77,500
Fair Value, Measurements, Recurring
Assets:
Cash equivalents	[1]	24,334	28,901
Marketable securities	[2]	23,549	20,222
Total		47,883	49,123
Fair Value, Measurements, Recurring | Active Markets for Identical Instruments (Level 1)
Assets:
Cash equivalents	[1]	24,334	28,901
Marketable securities	[2]	23,549	20,222
Total		$ 47,883	$ 49,123

[1] Included in cash and cash equivalents on our condensed consolidated balance sheets at June 30, 2020 and September 30, 2019. Not included in these tables are cash deposits of $101.3 million and $77.5 million at June 30, 2020 and September 30, 2019, 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 sheets at June 30, 2020 and September 30, 2019.