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Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($) |  | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Nov. 18, 2016 | Mar. 31, 2017 | Mar. 31, 2016 | Nov. 29, 2016 | Sep. 30, 2016 | Sep. 30, 2015
Schedule Of Investments [Line Items] |  |  |  |  |  |
Percentage of workforce reduced due to discontinued clinical program |  |  |  | 30.00% |  |
Cash and cash equivalents |  | $ 61,718,971 | $ 50,300,847 |  | $ 85,366,448 | $ 81,214,354
Short term investments |  | 24,910,492 |  |  |  |
Net increase (decrease) in cash |  | (23,647,477) | (30,913,507) |  |  |
Cash outflows related to operating activities excluding upfront payment from Amgen |  | (34,300,000) |  |  |  |
Cash outflow from investments in commercial bonds |  | 24,846,105 |  |  |  |
Capital expenditures |  | 6,653,158 | 500,634 |  |  |
Proceeds from the issuance of common stock |  | 12,691,937 | $ 25,544 |  |  |
Restricted Cash |  | 0 |  |  | 0 |
Short-term investment, gross unrealized losses |  | 130,319 |  |  |  |
Fair value |  | 24,780,173 |  |  |  |
Investments |  |  |  |  | 0 |
Fair value of contingent consideration obligation due to discontinuation of clinical trials |  | 0 |  |  | $ 0 |
Corporate Bonds |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |
Short term investments |  | 24,910,492 |  |  |  |
Short-term investment, gross unrealized losses |  | 130,319 |  |  |  |
Short-term investment, gross unrealized gain |  | 0 |  |  |  |
Maximum |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |
Amount insured in FDIC per account |  | $ 250,000 |  |  |  |
Property, Plant and Equipment, Useful Life |  | 7 years |  |  |  |
Minimum |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |
Property, Plant and Equipment, Useful Life |  | 3 years |  |  |  |
Amgen |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |
Proceeds from upfront payments and equity investments |  | $ 42,500,000 |  |  |  |
Amgen | Common Stock Purchase Agreement |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |
Proceeds from the issuance of common stock | $ 12,500,000 |  |  |  |  |
Amgen | ARO-LPA Agreement |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |
Common stock issued | 1,745,810 |  |  |  |  |
Upfront payment | $ 30,000,000 |  |  |  |  |
Amgen | ARO-LPA Agreement | Common Stock Purchase Agreement |  |  |  |  |  |
Schedule Of Investments [Line Items] |  |  |  |  |  |
Common stock issued | 1,745,810 |  |  |  |  |

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