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Organization and Significant Accounting Policies - Additional Information (Detail) - USD ($) |  | 9 Months Ended |  |
--- | --- | --- | --- | ---
Nov. 18, 2016 | Jun. 30, 2017 | Jun. 30, 2016 | Sep. 30, 2016 | Sep. 30, 2015
Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Cash and cash equivalents |  | $ 38,383,135 | $ 43,616,543 | $ 85,366,448 | $ 81,214,354
Short term investments |  | 36,754,754 |  |  |
Net increase (decrease) in cash and investments |  | (10,200,000) |  |  |
Cash outflows related to operating activities excluding upfront payment from Amgen |  | (44,700,000) |  |  |
Capital expenditures |  | 7,810,754 | $ 1,147,748 |  |
Proceeds from the issuance of common stock |  | 12,419,119 |  |  |
Restricted Cash |  | 0 |  | 0 |
Fair value of contingent consideration obligation due to discontinuation of clinical trials |  | 0 |  | $ 0 |
Maximum |  |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Amount insured in FDIC per account |  | $ 250,000 |  |  |
Property, Plant and Equipment, Useful Life |  | 7 years |  |  |
Minimum |  |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Property, Plant and Equipment, Useful Life |  | 3 years |  |  |
Amgen |  |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Proceeds from upfront payments and equity investments |  | $ 42,500,000 |  |  |
Amgen | Common Stock Purchase Agreement |  |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Proceeds from the issuance of common stock | $ 12,500,000 |  |  |  |
Amgen | ARO-LPA Agreement |  |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Common stock issued | 1,745,810 |  |  |  |
Upfront payment | $ 30,000,000 |  |  |  |
Amgen | ARO-LPA Agreement | Common Stock Purchase Agreement |  |  |  |  |
Organization And Significant Accounting Policies [Line Items] |  |  |  |  |
Common stock issued | 1,745,810 |  |  |  |

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