Summary of Significant Accounting Policies and Select Balance Sheet Information - Disclosure - Amortized Cost, Unrealized Holding Gains and (Losses) and Fair Value of Available-for-sale Securities (Detail) - USD ($) $ in Thousands |
Sep. 30, 2017 |
Sep. 30, 2016 |
|---|---|---|
| Schedule Of Available For Sale Securities [Line Items] | ||
| Amortized Cost | $ 31,817 | $ 22,019 |
| Unrealized Losses | (15) | (65) |
| Fair Value | 31,802 | 21,954 |
| Commercial paper and corporate bonds [Member] | ||
| Schedule Of Available For Sale Securities [Line Items] | ||
| Amortized Cost | 31,817 | 22,019 |
| Unrealized Losses | (15) | (65) |
| Fair Value | $ 31,802 | $ 21,954 |