Fair Value Measurements - Assets Categorized on Basis of Various Levels (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market fund deposits	$ 12,845	$ 13,832
Mutual fund investments	9	8
Total	12,854	13,840
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market fund deposits	12,845	13,832
Mutual fund investments	9	8
Total	$ 12,854	$ 13,840